Hi scooter85
I am sorry to read that you feel like her "whipping boy". BPD is a challenging disorder and many people with this disorder unfortunately do have the tendency to take their frustrations out on people close to them.
Could you tell us some more about your daughter's behavior and the traits she exhibits that make you think she has BPD? What would you say are her behaviors you find most difficult to deal with?
You mention believing your daughter most likely has BPD since she was about 15. Did anything happen around that time that coincided with the changes in her behavior?
As you are looking for new ways to cope I suggest you start by taking a look at the resources to the right of this message board. I believe they can be of some help to you and shed some light on what you're dealing with here.