Help! Manipulative sister in law

I need some advice

To put it bluntly, my sister in law is without a doubt the most self centred person I have ever met. When I first met her, there was no denying she was not a warm and cuddly personality and what she perceived as ‘banter’ was incessant and hurtful insults followed by long and obknoxious fits of laughter. Safe to say, she definitely wasn’t my cup of tea or someone I enjoyed hanging around with but that was as far as it went.
Over the last couple years however things have simply gone too far and have gotten way out of hand. To give some context, my fiancé has no parents and they do not keep in contact with many other distant relatives so they are each other’s only family members, meaning for years a lot of her bad and selfish behaviour has been given a hall pass and let slide as my fiancé feels guilty. However, that bad behaviour has since spiralled into downright toxic and manipulative behaviour and I really need some help.
Since I have known her, my fiancé being her older brother has acted as a parental figure and has been consistently about to / in the middle of / just wrapped up from doing another favour for her. Their relationship has always been take and no give at my finance’s expense and while it’s always been a big stress and pain point for my fiancé, he continued saying yes - jumping and asking how high to every single favour. Yet that’s their relationship and frankly none of my business. However, over the last two years her selfishness has gotten out of control and she has treated both myself and my fiancé like two personal assistants, TELLING us we will be minding her dog for 2 weeks or that we WILL be minding ‘a couple boxes’ for her and her husband in between a house move to save costs on storage, which came to be 14 huge boxes accompanied with a Christmas tree, enormous dog cage of which is we were told was not allowed outside or it would rust and everything from ironing boards, electrics.. you name it. To avoid spending on storage, we lost an entire room of her house to store all of this for 6 months during a lockdown where we were confined to our house. Incredibly selfish but worst of all we were never asked for we were TOLD she would be dropping up ‘a few boxes’ and possibly worse again, we didn’t even receive a single thank you. To give further context to this, she has more money than sense so not only was it a selfish move at face value, but there was absolutely no need for her to once again have dumping her problems on us be her first port of call. It would be pointless of me to go through every time she has done something like this in the last two years, but this is the most recent and solid example of her selfish behaviour.
Recently, things have come to a head. I am quite a docile and passive person and often put up with far more than I should to keep the peace. She is a toxic and quite bullying personality, so with I her I have put up with SO much bad behaviour and poor treatment because she is simply dangerous to go up against. She is incredibly rude and insulting to everyone she meets and people she calls friends, yet gets incredibly manipulative and says they don’t understand what she is going through if ever she is called out for her bad behaviour. If I’m brutally honest, since meeting her I have done nothing but be so kind and friendly to her and made an enormous effort with her, but mostly because I am intimidated by her and I am uncomfortable to be around her as you never know what her tongue will cut you with next. To add to it, she is worse on front of groups of people, but recently she took it too far. As I said since meeting her I’ve been nothing but over the top kind to her even when she absolutely did not deserve kindness, I did myself proud and continued to be nice to her. Months ago, we sat at a dinner table myself, my fiancé, her and her husband along with his parents, both lovely people. While we were currently down an entire room in our house because she dumped a truck load of boxes in our house without even asking and without any thanks, she chooses to ‘jokingly’ give out that we did not offer herself, her husband and dog a bedroom to stay in for the 6 months they would be in between houses!! To start with, this dinner was an exception as it was a wedding tasting for her but otherwise we had continued to avoid household meet-ups during Covid as I am high risk and since the whole thing kicked off they have been outwardly vocal in how little they took it seriously. Not only is it ludicrous for someone high risk to share households with someone not taking Covid seriously but the cheek to say that on front of a table of people when we have done so much for her without any thanks and just let her walk all over us quite frankly. I wanted to respond and say we currently have lost a room that was used as an office during Covid because you want to save money from storage so I’m not sure where on earth you think we could fit a bed and you and your husband and dog?! Yet as ALWAYS, in total intimidation of her I said nothing as her wedding was just around the corner. Fast forward only an hour later and she drunkenly splurted out that myself and my best friend ‘were total b—-ches when she first met us?! And there was the line. Bridge burned. No going back. To say I broke my back making effort and being kind to her even though her snow storm of insults and rudeness, would be an understatement. Never before has a more ironic insult been made so my fiancé who is ordinarily passive said that is unacceptable and couldn’t be further from the truth. He reminded her that my name and the word b—— had never been used in the same sentence, letting the idea that the same couldn’t be said for her linger in the air, but of course she isn’t self aware enough to have received the hint. I stayed silent once again and no apology followed the next day or ever for that matter yet for me that was the cut off point.
...and here we have the came to a heads moment. Not only am I high risk or Covid but it has come to light that my younger sister is INCREDIBLY high risk and I will leave it there but flag that it has been an incredibly tough few months all of which she is aware of. My sister in law and husband are in the middle of IVF and while I don’t deny it must be incredibly tough and stressful, it was always going to be used as an excuse for her to push our boundaries and jump onto the pattern of ‘use & abuse’ but label it as ‘support.’ Keeping in line with having zero respect and putting herself first, she has incessantly called over to our house unannounced often letting herself in despite my fiancé asking,begging, pleading,demanding her not to for years. You name it, every which way he has tried it and nothing has worked. The last 2 years however the unannounced door stops, have gotten out of control. Never does she show up alone either it’s with her husband so we are expected to drop everything and host usually for a couple hours with the two of them playing blind to everything from yawns, to seeing we were just about to serve dinner, to seeing I am in the of middle of work or just out of the shower or my fiancé saying how he doesn’t feel well. It’s not that they don’t physically see these things, it’s that they don’t care. Weeks ago, the very final line was crossed when in full understanding that we are not mixing households they turned up at our door at 10pm at night unannounced as always asking to come inside. When my fiancé said no as of our Covid situation (which pained him to do) she turned on the waterworks and essentially barged in and closed the door behind her. Within half a second the tears conveniently dried up and an hour and a half talking marathon began of her excitedly talking about IVF and her new house move while we stood there feeling so violated, disrespected and for me personally... uncomfortable as I was in my pyjamas and having a bad skin day. After feeling upset and disrespected by this for days knowing she did this not caring about how high risk myself and my sister are, just flicked a switch in me so I pulled myself together to send her a text which I got external opinions and encouragement from several friends - is it obvious I’m afraid of this girl yet?! My text was fair, calm and polite and explained while I am so there for her with anything she is going with, knowing how dire my sister’s situation is as well as my own in terms of being high risk, the other night put me in an uncomfortable position so could we please continue with meeting outdoors for now and please send a heads up text before coming over as without being any less supportive we were in the middle of a very serious chat ourselves and felt caught off guard.
Naively thinking she might be defensive but get the message, she instead responded by meeting with her brother (causing him days of stress) and saying I had no business telling her she has to give notice before coming over. First I politely asked and had asked her as a ‘friend not a sister in law but secondly it was because it involved me and my sister being high risk and no matter how many times my fiancé has begged her to stop she continued doing it!!!! Lastly I am a human and it is my home too but no, she made me feel like I have zero value, she doesn’t care about me or sister being high risk and worst of all told me her and her husband (who is afraid of her) are angry upset and hurt following my message and that the stress of all this isn’t good for her trying to get pregnant?! The stress of being asked to give a heads up? It’s just mind blowing. I contacted her to reiterate please come over as much as you like it’s simply a case of knowing how dire things are can you please give us a heads up first, but that doesn’t go along with her fictional twist on this so it has been ignored and we haven’t spoken in weeks.
Quite simply she is toxic beyond belief and I would like her out of my life for good bar Christmas and other events I can’t get out of. Any advice on how to achieve this without my fiancé being stressed or affected would be amazing.