Gf started self harming?

We have been in a relationship for 10 months. I cheated but we decided to try to move on from it. I don't think she is handling it well, ever since, she's been different, she's happy some days but other days she's a completely different person and gets angry at me and cries and brings up what I did.

I still want to work things with her because I love her, but I noticed she's been self harming. I know it's because of what I did and I don't know what to do.. It's been a really tough month.

EDIT: She has NEVER self harmed before. She just digs her nails in her arms. She has many scars. People may think this is nothing but I think it is as serious as any other self harm. She is 21.

She has never manipulated me nor guilty tripped me. Instead she feels like SHE'S at fault.