i don’t want to be involved in my friends wedding because of how she’s behaved for mine

I’m hesitant to post this but truly feel I need advice from people who don’t love me and know me.
I have a friend who I’ve had trouble keeping connection with, none of my other friends or future husband are a fan because she is a little unstable and I guess “toxic” as some would say. Nothing in her life is good enough for her, I have a hard time respecting her as a partner and parent because she will just storm out and not tell her fiancé where she’s going and disappear and lash out at him and her two year old to the point her two year old will say sorry for making her sad and ask her to calm down. She’s already “fired” two bridesmaids and threatened to fire all the rest of them because they hadn’t started up plans for her pre wedding festivities two years before her wedding date. She begged her fiancé to propose to her for a year, these “discussions” led to blow up fights where they would break up for a week and multiple times. But then she’d tell him he’d have to pay 1k in child support and refused to help him with their daughter saying he can’t do it without her and to figure it out and if they’re not together she won’t help with her own child.
Anyway, so I have a very hard time setting boundaries with her because I care very much about her daughter and we were friends in high school so to an extent I have a bond with her and I know what she went through as a kid. She decided to move her wedding up a full year and a half and now it’s in may. They’ve decided not to serve food and to have a cash bar and they want their guests to bring their ceremony decorations. They asked everyone to bring a dream catcher or wind chimes for their backdrop and are relying on guests for it. She was mad because she found out “if guests don’t pay enough tips to the bartenders” or buy too many of their own drinks she would have to do 20% of what we all spend if we don’t “tip enough” or “drink too much.” She’s expecting me to purchase an eighty dollar dress, which isn’t bad, but for my wedding she refused to purchase the dresses I picked (50-140 in price ranges) and got a ten dollar dress on Amazon and asked if it was okay. She asked me to book a venue for her bridal shower but she showed up to mine empty handed, with no decorations no gift and didn’t do any of the planning for mine. I was previously in an abusive relationship (a long time ago) and she expects me to get along with women who consistently undermined what I went through even after it came out he seriously injured his infant child (the woman after me and his) they said they believed it may have happened but it “probably wasn’t as bad as I said.” And she said she could see how they’d think that. I feel like I almost have a trauma bond to this person but I’m being asked to buy an expensive dress drop 150 on her bridal shower when she DIDNT contribute to mine and then had the nerve to vent and complain about all the work my other bridesmaids put into it saying that she’d rather have no bridal shower than mine and that she knew I wouldn’t do that to her when we plan hers and that if her bridesmaids get decorations from the dollar general they’re fired, she said that to her other bridesmaids. She told me she was pregnant on my bridal shower day and spoke about her wedding the whole time which didn’t bother me until she went off about how horrible my other friends were. But I was happy with my bridal shower. I don’t want to be in a different city from my fiancé for a weekend as it is, let alone to spend a bunch of money on the hotel I’m required to stay at the night before and after, pay for my own drinks, get myself back to the hotel somehow, not sure what else she’s cheaping out on if she’ll feed anyone at all that day or if I am supposed to drink on an empty stomach? Like is there a time window for me to pay for my own food in a drive through then? She literally only bought three of her bridesmaids bridesmaid t shirts and sent the rest of us a link to buy our own because she “couldn’t afford it.” But I spent 50 bucks on each of my bridesmaids including her, not to mention a yacht fully open bar champagne cocktail cruise excursion, catered breakfast with gourmet pancakes morning of, etc. I feel like I have no respect for this person. Whenever we’re together I help her daughter make brownies and take her to the park and for picnics and I pay for everything. Whenever her and her spouse to be break up she camps at my house for a week with her kid and I pay for everything and talk her off the ledge while gritting my teeth because she does not talk to me any other time. I do realize that it says negative things about me that I’m even involved with all of this, but I did try to say no to being in her wedding citing my own wedding as the reason but she didn’t accept that. And now I don’t know how to back out but I don’t want to be apart of this I don’t think the relationship will survive and it doesn’t sound like a good time. I feel sorry for her daughter and fiancé because I feel she’s manipulative selfish and entitled. And I don’t like that in this relationship with her I find myself keeping score and feel I’m a better person outside of this friendship. I’m not perfect financially but I have managed to host my own wedding and treat my bridesmaids like I love them and value them and have been grateful for what I’ve been given and not asked for anything more