Just looking for some advice or support

I went nc with my uBPD mom last November, and I am not ready to face her yet.
My sister's graduation is this May as well as another ceremony I won't specify for privacy. I want to go to support her, and I was going to be involved in the second.
I decided that it would be best if I didn't go. Because 1. I'm not ready to face my mother who will be there, and 2. That time should be about her, and if I'm there it'll be overshadowed by the conflict between my mother and I. (I think the whole time would be her making a show of either ignoring me or begging me to forgive her.)
She texted me this weekend the finalized dates for those and I'm going to talk to her possibly tonight about why I shouldn't/can't go. I haven't had the conversation with her about why I went NC so I'm stressed thinking about this, and almost cried a few times.
My plan for the call is:
1. Ask what she knows about what happened between my mom and I. And clarify why it matters to me that I have space right now.
2. Explain why I think it's better that I don't come (mostly that I don't want to turn it into a drama).
And having my boyfriend there to support me, though quietly so I'm not continuing my mother's narrative that he's controlling me.
I'm not sure if she'll try to convince me to come. Or if she'll be like my other sibling and want me to just "make peace" or "confront it". I like to please people and compromise, so I'm easily swayed to give up information or agree to plans (hence the boyfriend support). Maybe she'll be totally understanding.
I feel bad saying no to her when she deserves better and when it's something I would otherwise be eagerly going to.