What can I do for my girl friends parents who yell at her everyday. They made her self harm in the summer. I didn't care but now she cries about it. How can I help her?

At times like these it's a really complicated situation. Since she's only your girlfriend now, there is nothing much you can do about it. It's her parents and if you interfere, it may worsen things or may even create misunderstandings. So at times like these, the only and best thing you CAN and SHOULD do is be there for her. Acknowledge her feelings, help her with whatever she needs. So whenever she feels unheard or goes through something bad at her home just be there for her while she decides for. Often times we don't need someone to help us, we just need someone to be there for us. This is what she needs so try and do that. Be empathetic towards her. Be a shoulder that she has whenever she needs someone which she clearly doesn't have at home.