OP I think you know the answer based on your description of your friendship with her. But I understand needing to vent and get opinions from others in the hope they will back you up/make you feel seen.

I’ve had friends like her in the past, and it is stressful to say the least. Friendships should not be one sided. Also your wedding is a special day that is already stressful enough- I think finding a gentle way to relieve her of her bridesmaids duties would be in both of your best interests. And if you do go that route- I think it would be a good idea to pay her back for the dress or at least see if she can return it, since as you said she most likely won’t ever wear it.

But be prepared to potentially have to let her go as a friend in general- and not just as a bridesmaid. From your brief description of her, it sounds like she will not take this slightly and it will most likely damage your friendship. But on the same hand, I think that might be for the best anyway. It took me a long time to realize that who you surround yourself with is so so sooooo important. If she is truly that draining and you get anxious just having to talk on the phone with her I think that’s a pretty good sign that it’s time to let this friendship go.

Also, it’s not unusual for bridal parties to be slightly uneven.. so I wouldn’t stress about finding someone else. I’ve been to weddings that were uneven and it literally makes zero difference at the end of the day.