something happened that caused me to have an outburst at her in a fit of anger, leading me to confront her with admittedly some harsh words.

We exchanged some angry texts after that and the following day, we only had terse conversation without fully resolving the argument - which I had thought would happen eventually.

Instead of dealing with the argument, she texted me at 2am on the night before the bridesmaids brunch that I had planned, saying that she is declining to continue participating in my wedding as a bridesmaid. I felt completely betrayed because she would choose to retaliate in this way.

YTA for being a bridezilla. You started an argument and then expected her to resolve it because you need her. You don't get to talk to people however you want and assume they have to suck it up and participate in your wedding no matter what. It's not retaliation; it's just the consequences of your own actions coming back to haunt you