YANBU.
My chief bridesmaid / best friend did similar. She didn't ask me to be her BM (her choice, but it hurt), I then got shoved out of organising the hen weekend (that she'd given me as a consolation prize for not being BM), due to her befriending an utterly vile woman at her workplace who just took over everything.
I was then asked to organise the local hen night, as vile woman was now organising hen weekend and it was abroad (best friend insisted my own hen weekend wasn't abroad as it wasn't fair to guests). On the hen weekend, vile woman started on most of the hens while drunk and had a huge run in with best friend's sister.
On the day of the wedding, vile woman turns up in a 50s style white dress, best friends wedding dress is 50s style.
Got to reception, we'd been shoved on a table so far at the back that we couldn't hear or see the top table. Vile woman was on a table at the front (I swear she got involved with table planning) and proceeded to drunkenly heckle the speeches.
A few months after the wedding, my best friend realised this vile woman for what she was and dropped her. I was just gutted that it ruined my memories of her hen and wedding.
Try not to let it poison things if you wish to maintain a friendship. It's a bitter pill to swallow, but you need to ask if it's worth losing her over.