Tattoos aren't listed in the criteria for self harm. Although I once had a friend who'd etched something in her chest and I went with her for a tat to cover it up. The self etch to me, self harm. Tattoo, not self inflicted injury,
Everyone classifies the pain(or not so painful) of a tat, different. If she chose to place them not on display, her choice. Lots of people don't show them off, daily.
I occasionally show off one, not the other. It is what it is.

If using the diagnostic criteria to ask if bpd, might get more positive response.

Learning effective communication skills to be supporting seems a better approach.