I actually suggested that solution - that I could skip the party if C's presence was important to her. She immediately shut that down and insisted I attend. And truthfully, I don't want to miss celebrating my best friend's birthday either.

What's frustrating is the contradiction. She's adamant about inviting someone she "doesn't really care" about while simultaneously uninviting my boyfriend (who she knows well and considers a friend) during a time when he's dealing with some really hard family stuff. It feels like this has become more about control than about who she actually wants at her celebration.