Mother in law constantly crying

So way before my fiancé and i have gotten engaged my FMIL has always been a cryer. Ever since the wedding planning it’s all gotten worse. I get that the first wedding is always going to be a little harder. But it’s getting out of control. She has almost meltdowns about everything. She can’t even listen to one song all the way through without sobbing. It’s honestly so annoying. We were trying to decide on a mother-son dance song. My fiancé honestly does not want to do it, but since I’m doing a father-daughter, i thought it would look weird if they didn’t do a dance. So i texted her asking her if she has any song ideas and she immediately started crying. Like it was just a simple question!!! Then she comes home and can’t even play me any songs without crying. I can’t even have a conversation. It drives my fiancé and i both crazy. I don’t want her to have a melt down at the wedding during the dance because it’s just embarrassing and she makes it about her. I mean we are celebrating my fiancé and i getting married. This isn’t a sad time. I mean, yes it’s bittersweet for all parents, but my mom has not once had a freaking breakdown like this. Like should we opt out of the mother-son dance?? I really don’t know what to do. I’m sick over it. This is our special day and honestly she makes me feel guilty for marrying her son.