You cant control what she does, you can only control what you will allow yourself to be exposed to.
When she is upset she wants to project that upset onto someone, you.
If you are allowing yourself to be visibly upset by her actions then you validate the action as a way of projecting her hurt. That soothes her, so she will continue to do it.
Deliberately cutting you out is a type of abuse. Abuse requires learning healthy boundaries and how to uphold them
BOUNDARIES - Living our valuesBelieve it or not even though people with BPD try to trample over other peoples boundaries they do not respect those who allow it to happen.