Hi Murbay,
I've seen a few posters here in facebook relationships with a pwBPD SO that decided to actually not having a FB relationship anymore. Consider breaking off the facebook aspect of the relationship if you see it as a destabilizing factor. It is a drama prone area - you flick a switch and it is black&white decision. That decision is communicated without you having to face the person. The message arrives through a channel with some delay and hits the other person in a random emotional state. Why should this ever be working in a smooth manner unless the other person has a certain degree of self restraint?
It sounds very childlike and perhaps immature though it does help me to identify what mindset she is in as that is all I have to go off when she does this.
Indeed, while it seems to be a "big" b&w decision it contains almost zero information. Ignore FB and use other, richer communication channels like email or phone.