Awkward invite situation.. guest inviting themselves

This is beyond tacky of her to do. I would just straight up tell her. She might think it's rude but what she did was ruder. Warn your bridesmaid what you plan to do before you do it. She'll (hopefully) be mortified that her friend did this and support you fully. I would not put it on your bridesmaid though as she could feel caught in the middle.

I cannot get over how rude and forward she is! Personally, I would respond and just say something along the lines of "Unfortunately, we are having to limit our guest list to family and close friends". You could also maybe throw in something about missing her too and to let you know if she's ever in the area and you two could get together and catch up. If she gets upset about it, oh well. There really is not much else you could do. I'm sorry you are having to deal with this!

I agree with others that sometimes you just need to be blunt with rude people...and you need to do it yourself; this is not your BM's responsibility and you'll potentially put her in a awkward position with her friend and it likely won't put an end to the conversation. For daughter's wedding we had two long-term acquaintances (of us, her parents) who assumed they would be invited and just ignoring their awkward inquiries didn't stop their even more awkward "hints." Finally, we had no choice but to tell each, point blank, that they were not going to be invited. We said something along the lines of, "Unfortunately, the B & G weren't able to invite everyone they would have liked to, so they've prioritized family and their closest friends. We're sorry, but you won't be invited." One of the two offenders took it fine; we think he just has really awkward social skills, so he didn't really intend any harm. The second had ulterior motives for wanting to attend that had nothing to do with caring about the B&G; I think she was mad I said "no" and she hasn't talked with me in nearly two years.... No big loss! Good luck!