Flaky bridesmaids

I haven't read ALL the responses, but did see some and some of yours. My comments are limited to my experience with gaslighters AND flaky bridesmaids:

You are looking for advice and validation b/c she is GASLIGHTING (your words). This is a gaslighters specialty - they make you feel crazy and like you are wrong. So you have to ask others if you are crazy and wrong. You are NOT. Do NOT LET HER make you feel this way/ do not let yourself feel this way.

Secondly, I had a bridesmaid show up late for hair and makeup. She told me the night before she had a last minute showing (she's a real estate agent) come up and she didn't want someone else to handle it (she is a team lead with five other people that could cover for her). My mom is a real estate broker, so I know how these things go, but come on, she could have had someone else do the showing. I didn't really care, I just rolled me eyes b/c it was expected and why I had her doing hair and makeup last. She also bailed on staying the night at a hotel on a friend who needed the financial help. In the end, it's like you said - it showed her disregard for me and my fiance, and how little she cared about her obligations. After a year of planning and alllllll of this and other things, she's the one bridesmaid I know I'll lose touch with. I have tried to go out to lunches and dinners with her and she cancels and doesn't respond to texts or phone calls. If I could do it over, I probably wouldn't have asked her to stand up anyways.

Long story short, do you want to be friends with someone with such disregard for you and your friendship, and important things in your life, that GASLIGHTS you? Nope. Move on.

She is a terrible friend. Kick her out!

Got a big dude friend? Someone who is not afraid to take charge and be intimidating. Give them her picture and if she's spotted, have them escort her out. I've got people ready in case the crazy shows up. We also have security that is required by our venue. If you do...give them her info. That's what they are there for.

That's insane. Returning at noon the day of the wedding is a joke, knowing she has to get ready. I'd tell her to show up at 8 or not at all.

Seriously? That is absolutely crazy to plan a trip like that!

Literally the only expectation as a bridesmaid is to be present for the rehearsal and at the ceremony in the attire of your liking, and she can't even do that. I would suggest that this friend not be a part of the wedding party, because obviously she is acting as if she is simply a guest with better things to do prior to and the morning of your big day.

Oh no you're totally in the right.
Being a bridesmaid means being there for those things. If you prioritize something else over them, it means you aren't close enough to be a bridesmaid (or hey, maybe its something important, it happens) and should say no. Or throw the ball in your court. "Thank you for asking me, I have this trip planned that weekend and I won't be back until 12 the day of your wedding! I can't move it, but I love and support you and want to stand with you, even if I can't be in the photos. If that is a big deal for you I totally understand, I would love to just attend as a guest, it's whatever you decide!" That's what she should have said. It isn't a big deal that she is busy. Really, she could have downpayments down for something or it could be a big deal with family she's attending. But it's a huge deal she's pretending like it's now up to her if she is in this wedding. "Sorry I'm missing all the things, I am telling YOU that it's no big deal that i'm not doing anything you ask!" uhhh last I checked, when it's her wedding, she can decide what is and isn't a big deal. And honey...this is a big deal! Being stressed out about if she'll even show, what she'll look like, if she'll continue to flake, her missing the photos...tell her it's not that you don't love her and want her to be a bridesmaid, but if she can't be there at the night of the rehearsal dinner, then you need her to attend as a guest. ( I would say tell her 8 am, the time for hair and make up but I would worry she would still flake. She could say "fine I'll leave early and be there at 8" and still not do it. If you say the rehearsal dinner it is clear she has to choose you or the trip, even though missing the dinner at the end of the day isnt huge) Tell her she's still welcome at the bachellorette party if she would like, and you won't be expecting her to help with anything else now that she is no longer standing with you, it's not that you don't want her to be a part of things it's just clear she doesn't have the time for this commitment that weekend and you hope it doesn't effect your friendship.

Also, if she already bought a dress...I wouldn't feel obligated to reimburse her. She knew about this trip and should have pulled out on her own, she should have never said yes. If she's the kind of person where she's dramatic and is going to stop being your friend after you tell her she can't be in it (which should not be the case. A normal person would 100% understand why they can't be in it and would have never said yes. The fact that she's putting you in this spot is astounding) then don't reimburse. If you want to keep her on your good side, think it would help patch things up if she's sad about it, and have the budget, then maybe I would reimburse.

Well she sounds like the type you have to cut off completely. It won't be fun for you at all. You used the word gaslighting so you already know what your up against. Yikes