Hi rockinro and welcome to BPDFamily

Now that your sister has been officially diagnosed, you do at least know what you are dealing with. It is unfortunate though that she at this point seems to deny her diagnosis, is not taking the medication she has been prescribed and does not want to participate in DBT.
What led up to her now being officially diagnosed with BPD and depression? Was there a specific event leading up to this happening now?
I think it is wise that you indeed also consider your own emotional well-being since dealing with a disordered family-member can be very challenging and draining, particularly when the family-member does not really acknowledge her/his own disruptive behaviors..
You mention the support she gets from your other two sibling and friends. In what ways do they support her? How do your other siblings feel about your BPD sister's behavior?
The Board Parrot