Introvert behavior in pwBPD is often more a consequence of social anxiety than anything else, seeded by a fear of failure.
However when they make friends they are so relieved that they go overboard into idolization. This in turn can give come on messages to the other person. This leads to this issue you raised.
A few years back she was raped by someone who was a very new friend that we met. We became friends with this person quite quickly and it happened only within 2 months of meeting him. Being BPD she has a tough time making or keeping friends, and the guy was her first real friend in a very long time. She hung out with him a lot and ended up hanging out him with without telling me, and during 2 of those times was raped. We cut ties(no police conviction due to complexity) but since then shes only made one 1 other female friend.
My wife did the exact same thing and filed a police report, then withdrew it due to sickness(?). To this day if I am to be honest I could not say for sure if the claim is true or false. All I know is she felt "abused", how much she coloured this up I will never know.
A pwBPD can put someone on a pedestal very quickly, then one day put a rope around their neck and kick the pedestal away. All on a perception.
When it comes to friendships there will never be a healthy balance. There will be white knights who meet their needs, then when they dont, maybe by having strong boundaries, they turn into slime balls that have just crawled out of the cesspits. Do not get too engrossed in all these extreme dynamics, otherwise you will be so busy "supporting " her that you have no life of your own.
ie Stay off the roller coaster and concentrate on your own life. It will make it easier to provide the balanced support she needs rather than just reacting to drama, of which there will an endless supply.