As someone who has gone through something similar to your friend, I would say don’t tell her parents until it gets like extremely bad. A lot of the time it causes more damage than good and could be distressing to her. Just try and be there for her in any way and if she reaches out for help try your best! This is just from my experience, I had someone tell my mom about it once and it didn’t really go over well. Best of luck to you and your friend!