Opinion and Advice

I know this isn’t helpful, but your friend is not considerate of your needs while still wanting to do this for you. It’s going to be a “look” if you pass out and have to miss the festivities because you’re in L&D and heaven forbid something happens to you and baby. Wear compression socks until you have to walk down the aisle and after ceremony and pictures. Maybe a minifan to hold behind your bouquet. With a history of fainting, I’m very nervous that you can’t sit. How long is the ceremony?

Oh I unfortunately this gal is very inconsiderate but always has been kinda person she is not in a mean way but just who she is always about her it’s a personality quirk! I want to support her as much as I can but also be careful about baby! Ceremony is non religious 20 mins max but it’s fully exposed and no tent! The fan is a good idea.

You gotta do what is best for you mama. Would the bride rather have her "look" altered by you wearing compression socks, or have one of her bridesmaids faint. Totally guessing, but if she is more concerned about her look than the safety of her friend, I can see her being mad that the spotlight wasn't on her if something did happen to you (God forbid). Personally, I would advocate for myself harder and if she isn't having it, I would just become a guest instead of a bridesmaid. No need to put yourself and your baby in danger to uphold someone else's look

Do what’s best for you. But if you do plan to go, don’t lock your knees when standing.

If you’re not able to stand for 20 mins you should be getting regular medical help and/or on bed rest. I’m a wedding coordinator and also 31 weeks pregnant in the heat of summer with pretty bad PGP. Fan, cooling neck towel, chair nearby during photos for when you’re not in the photo. A chair open in the front row for you to quietly excuse yourself to sit if you absolutely must. Wear your socks until it’s time for walking down the aisle and photos. Wear your hair up if you can. Lots of hydration, protein snacks. Support band like a serola belt under the dress or supportive undergarments that will help with the back pain.
But I’m more concerned that you are going at all if standing for 20 mins isn’t doable without fainting.
Also the way you respond about her sounds like you don’t even like her that much. If you must go, maybe just be a guest and not a bridesmaid, but this late in the game I’d be prepared for emotions about it.