Welcome to the Parenting Board gramma_cocoa.
I'm sorry that your daughter is posting hurtful things on social media. People with BPD often do this to get others to help them justify their feelings... .it is their version of the truth based on emotions. They don't accept accountability for their actions and asking them "why" will only get a defensive response.
PwBPD (people with BPD) experience attention to others as taking something from them... .they don't understand the concept that love multiplies and doesn't divide so any attention/accolades/love/admiration/kindness to others feels like it is taking away from the attention/accolades/love/admiration/kindness that belongs to her. She also has a deep sense of shame and unworthiness and on some level doesn't believe she is worthy of love. Combine these together and she will react negatively. It is her illness.
Society often blames the parents for the way children/adult children behave. Mental illness has hereditary as well as environmental roots, have you seen this?:
Did I cause this?Being well educated, skilled in responses, accepting of our child's illness, supportive (not enabling) and compassionate are things we work on here to get the best possible outcome for ourselves and our kids. We are glad to have you here learning alongside us.
lbj