I think my friend might be cutting?

So today I was hanging out with my friend, and we were sitting on a couch. I looked at her leg briefly, and noticed a spot where there were a few scars. They were really small, maybe only 1/2 an inch each, but they were all in the same spot together on her leg and there were about 10 or 15 or them. The reason that made me really think that they were cutting scars is because she kept pulling her skirt down or crossing her legs so I wouldn't see. It just made me really scared for her, and I didn't know what to say. I wanted to tell her that she shouldn't cut and that there are so many people that care about her, but if she kept trying to make me not see them, then she obviously didn't want me to know about it, but I really want to help her. What should I say? Should I keep dropping hints until she admits it herself, or should I just flat out say "I know you're cutting, and it really scares me"? I mean, I really don't want her to get mad at me if I say that. Also, another thing is, they looked pretty old, like, none of them were open cuts, they were scars, so maybe I just shouldn't say anything if she's stopped? I don't know. I'm really confused and scared, what should I do?