As people have pointed out, suicidal thinking/behavior and self-harm are not exclusive to BPD. Indeed, the new diagnostic manual proposes two as of yet undecided diagnoses for both suicidal behavior and self-injury that would be on their own without necessary connections to anything else. So it may not even be indicative of another disorder.

Diagnosis is very complicated. And BPD is a very complicated condition that has a range of things associated with it. People at in various states may present as if they have BPD, but actually in their typical state do not meet the criteria. That happens with people with chronic/complex PTSD and dissociative disorders too. People can have attachment issues that affect their behavior to produce BPD like symptoms, but they do not reach the level of a disorder per se.

But I'm curious. If she was in the hospital and also is on meds then doesn't she already have a diagnosis? Is it that you don't know or that you disagree? Having a diagnosis seems like it is something that is personal and also pertains to health issues so is private.