Sounds like a bi*** to me! I don't even know if I would be able to let that go, so kudos to you. Not that I'm trying to bring you down, but you also are gonna be kinda screwed on your wedding day because she is obviously unreliable. Most bridesmaids are happy to help on the big day, but this one is obviously just not into her job.

Most importantly, don't let her ruin your wedding day. Just ignore her if she pulls any other stunts like this, you don't want to remember your wedding by the unreliable, careless bridesmaid you had.