With any disorder, not everybody has every variation of every possible symptom. It isn't fair to suspect someone on the basis that some people who have the same diagnosis have a symptom expressed in a certain way. That isn't about your girlfriend at all.

Trust is very important in all relationships. Also, people tend to get into relationships with others who function on a similar level to themselves. She's going to therapy and working on her problems. What are you doing to work on yourself and keep the relationship satisfying for both of you? You might find it interesting to read about the types of partners who typically hook up with people with BPD. Not saying it's necessarily you, but it could be enlightening. Relationships are a two-way street.