Step Families Support Group
Traditionally, a stepfamily is the family one acquires when a parent enters a new marriage, whether the parent was widowed or divorced. This community is focused on many of the relationships and issues that may arise within stepfamilies where you may find answers from some members and you may help other members with their questions.
If you feel you really were friends, talk to her and ask her about it. I don't agree with what she did, but try your best to withhold judgement and give her the benefit of the doubt. Maybe she was really trying for it not to matter to her, and she lost that battle and her real feelings spilled out. But you are still going to have to have an ongoing relationship, so it's best to try to fix it than to write it off and think the worst.
I would let it go. I don't know that I would even address it with her. She knows what she did and hopefully is embarrassed by her behavior. I would suggest that because of the display that maybe your "friendship" be a bit more limited and maybe not so close at least for a while.
Also, how you handle it will set the tone for future conflicts.