“why the fuck is she acting like this she's literally asking for it” — answering the question.
The borderline personality is in a state of panic over being abandoned, rejected, or betrayed. They strike first, expending colossal amounts of energy out of nowhere because they live in a permanent state of fear. Aggressive trolling is the built-up armor of an anxious individual who remembers themselves as weak; hidden behind it is a raw nerve that is desperate for acceptance.
Having experienced rejection without the resources to cope, this person is deathly afraid of opening up again: they lack the strength to heal the old wound, and a new one would prove fatal. Any calm interaction triggers panic within them: they unconsciously look for a catch, perceiving your relaxed demeanor as nothing more than the calm before the punch.