I'm not trying to say or assume that this girl's scars are NOT from self harm, but . . . .be very careful about what you assume/presume about a stranger. Something that looks like it's gotta be from what you think it is may not be.
I have some nasty scars on my arms from quite literally two frightened cats who (serially) went ape-shit and I had to deal with them. One cat got extremely upset by a move, another cat very similar circumstances and now needs Feliway to keep him calm. Don't underestimate a domestic cat -- they are capable of turning you into something that looks like a swamp alligator got hold of you. Not even lying here.
A few years ago, someone pointed to the baddest scar and asked me point blank "So you self harm?"
I have never self harmed in my life and cannot imagine doing so -- I FAINTED at the sight of my own blood the night my cat ripped me open. I'm one of those people who could never be drawn to that activity. But someone was convinced that's what it was.
So I'm not saying this girl was attacked by a cat like me, lol, but what I'm trying to say is, self harming is not the only way someone might wind up with bad scars. Another case in point: a friend had horrendous scars and it turned out to be a skateboard accident.
Someone also might conceivably have been attacked by a spouse or partner. Like self harming, that's not something they probably want to chat with a stranger about.
Again, I'm not presuming to know what that girl's deal is -- maybe you are completely correct in your guess.
But just saying -- something can look like something and it genuinely is not that thing. I'm mortified about my scars because I know the world today goes straight to "she's a self harmer!" and that's not what happened to my arms. It's become an issue for me, particularly since nobody believes me even when I tell them exactly what happened. It just sounds like a made-up story and this whole thing about not being believed makes me so angry.
Don't open up a can of worms with this girl. Especially if in fact her case is indeed actually self-harming.