I am 13 and i am trying to help my friend out with her math because she is teaching me art.
If your friend likes art, you can use that to motivate discussions about math. For instance symmetry is a concept that has a lot of art application, as do triangles, squares, etc. It all depends on what subject she is studying. You can find interesting lesson plans and tools on teacher web sites, which are full of suggestions about how to motivate students. Try the teacher channel, for instance.