Wedding drama

Some people are competitive by nature. It is not your fault for bringing this to her attention because it's annoying. You can simply say, "while you're competitive, I am not about my wedding. It's a day for me and my partner. We can both be happy for each other, but I'd rather not tell you more information about my wedding because in the past you've had negative things to say." Don't ask her to be a bridesmaid until maybe January or this will bring you anxiety.

I agree with Imani, although I do find it odd that she tried to secure the same venue as you only 3 weeks before. If you feel this strongly about the way she's acting, and she isn't receptive to listening, I'd suggest 2 things -

1. Look back on your conversation and take responsibility for any missteps you may have had...was your tone maybe a little too harsh? Did something come out wrong? Is there a better way you could have phrased x, y, z? While she is obviously doing things to upset you, it can be of great benefit to approaching her with the respect that YOU deserve in order to set the bar for what you expect from her.

2. If you genuinely feel like you were kind, understanding, and you listened to what she had to say during your conversation when you approached her, I would deeply reconsider her place in your wedding. If you have a friend who is deaf to your feelings and makes you feel like your wedding choices aren't good enough, are they really your friend?

I agree with Imani too.

Also I'd stop sharing details with her, to decrease the one upping feeling that seems to be happening.

Since she's so competitive about your weddings, I'd take it as a compliment that she tried to book the same venue (and maybe take a little petty enjoyment from the fact that it was already booked lol). Going forward, I'd just stop discussing your wedding with her. Either say you don't have something done, it's a surprise, or you're still weighing options. If she presses, say you're not sharing any more details and leave it at that.

Some people take a while to recognize that just because someone likes something else, it doesn't make it bad or wrong, and that having different ideas doesn't make it ok to be critical. Everyone has their own taste in weddings, so try not to let her negativity cloud your appreciation of your own vision. You did the right thing by saying you're not in a competition. It's on her to realize that now.