The exact cause of BPD is still under a great deal of research. We do know that trauma and emotional neglect is a primary suspect. In the case of a mother with NPD, the emotional neglect and abuse would be very significant. As we form our view of the world we take much of the experience from our caregivers. If one of them is damaged significantly, yes, the trauma that can result can alter our image of who we are; cause us to think of ourselves in an unhealthy way, and push us to try to feel the love that we never did.
It is great that you are going in to counseling for BPD/ You most likely need the support and emotional security that this can offer. You re right, medications rarely help a trauma that was caused in our childhood years through the self centeredness and egocentrism of an adult, but you can recover from it with the right treatment.
A resource that has helped many people in your situation is a book that is one of my very favorites. Adult Children of Abusive Parents by Steven Farmer. In it you will see the mirror of what your mother did, but it is also filled with ways to change your thinking about you....This pattern of abuse and emotional neglect was not your fault, but you can escape the impact of it. Please think about getting this resource. It is wonderful and inexpensive on places such as amazon.com. With this and counseling of the type you mention you have a very solid opportunity to recover, Steven