Hey.
If it is non-lethal (not very much risk of being lethal) then she shouldn't really have an obligation to tell anyone. There are quite a number of people who self harm. For a variety of reasons. Possible reasons (not exhaustive) include:

- To feel calmer / more grounded
- To regulate intense distress
- To outwardly express inward pain

etc etc.

She will probably want to talk to you and try and try and help you figure out (if you don't already know) *why* you do it (what the effects are that sustains it).

And then you guys can work on alternative ways of achieving the same effect...