TL;DR - I've chosen not to spend the night before my BFF's wedding at her apartment despite telling her I would previously. I haven't told her yet and I'm feeling pretty guilty even though I know it's the best option and need some help in treading carefully 
The Background - My best friend from high school is getting married in two weeks out of state from where we grew up and where I still live. It's a very small, mostly family backyard wedding which is 100% her. Because it's so small I'm her only friend from home that's invited and can make it and I'll also be her only attendant.
Originally I was going to fly in the Friday before and spend the day hanging out and doing pre-wedding prep (maybe mani/pedi type stuff) and then spend the night at her apartment and help her get ready in the morning for the 11am ceremony. Last week while we were talking she apologizes and says she won't have the couch free because her parents have decided to spend the night with them Friday as well but she's working really hard to find a blow up mattress or she and her FI will buy one since they wanted one for camping anyway.
She really really wants me to spend the night because we haven't seen each other in years and I was looking forward to having extra time with her as well, but this situation makes me want to run for the hills. Just off the bat, that's five adults in a one bedroom apartment, one bathroom, three women one of which is the bride, trying to get ready for a morning ceremony. (And blow up mattresses are uncomfortable). More personally, I hate her family, especially her mother. I've even tried thinking about it in hindsight, that I was just an anti-parental teenager (I wasn't), but I still hate her and what my friend had to put up with. BFF moved across the country to be with her now-FI and I was so happy for her to get away from her family and join his.
I'm sure I could tolerate the wedding and the Friday pre-wedding things, but overnight (or even Saturday after the wedding, which was offered as well) would put me over the edge. I've already booked the extra night at the hotel I'm using Saturday, and a rental car as well for added independence, but I haven't told my friend yet. I'm dragging my feet because I don't want to let her down right before her wedding, and it really shouldn't be a big deal, but part of me wants to not tell her and then just be like "K Goodnight, see you tomorrow!" after hanging out. Would you care if you were in her shoes? How can I tread lightly and not become a "terrible bridesmaid!!" story on here? Am I over thinking this? 