Hi Rayi,
It sounds like
SET (support, empathy, truth) statements might help you talk to your daughter? There are some really helpful examples of SET in the book I Hate You, Don't Leave Me, which seems to be ever so slightly more tailored to romantic relationships, though I found the SET skills particularly useful with my SO's D19.
Support and empathy statements can help reassure and soothe some of the emotion states before presenting the truth, especially when dealing with double-bind situations.
Also, it sounds like asking
validating questions might be useful during those conversations when she is spinning and you (rightly) see she needs to solve things for herself.
It's good that your daughter will talk to you

Is she diagnosed with BPD? Does she live with you?
Glad you found the site, and hope you'll share more when you feel ready.
LnL