You can find a list of symptoms in the dsm, but generally your therapist or pdoc should be the only ones to diagnose. If you feel you fit some of the symptoms, talk to your t about it. There really isn't much purpose to a diagnosis except insurance payments. If you feel you might benefit more from, say dbt, then you can always just ask about doing it with your t.
I think bpd can taint other provider's views, and it's not exactly a diagnosis I would go looking for unless I needed insurance to pay for a particular treatment. There's still a ton of stigma around bpd with providers. Also, much of it can be better explained by trauma much of the time. I have found many trauma therapies also make use of dbt and cbt, so treatment kinda overlaps already.

Don't forget why you're there, it's to UNburden yourself, not protect her from being burdened. She's a trained professional and can definitely handle you.