One could say that it's typical BPD insecure behavior due to fear of abandonment. Suggest you decline to participate in responding to such allegations and, instead, just validate her insecure feelings.
A pwBPD have an innate fear of rejection and anticipate that they will be rejected real or not, I'd like to add that a pwBPD don't trust themselves and others, you'r inadvertantly giving her attention by defending yourself, negative attention is still attention and re-enforces dysfunctional behavior.
A valuable tool to minimize and eliminate conflict is to not JADE, don't Justify Argue, Defend or Explain, my ex wife may believe that the sky is red and I could argue with her exhaustively that the sky is in fact blue, her reality is as real to her as my reality is to me, this is what she's accustomed to. I'd also like to add that another criteria for BPD are rigid thought patterns, we can get bogged down with trying to explain or defend against a pwBPD's magical thinking.
Also keep in mind that you don't to validate the invalid, validate something that is valid if it's there, with that in mind, I will say things once to my ex wife, maybe twice but if she keeps asking, I don't JADE and the conflict ends because it takes two and a boundary is that I don't participate, she can think what she wants to think, it doesn't change fact.
Don't "JADE" (justify, argue, defend, explain)A 3 Minute Lesson on Ending Conflict