hmm, I imagine Diana would be into fashion like designing jewelry, clothes, shoes and then donate a lot of that $ to charity. She (like me if I was very rich) would like to supervise those charities and make sure the $ reached the people in need like children and the elderly and people in need in general like shelters.
I also imagine since she grew up in a beautiful island that she would love the arts, especially painting and music. She also likes sports, but it's not easy to be in teams because she's too tough lol, so she is very careful about that.
I think she would also love to read (I think she did in the movie). Maybe she likes to go to public libraries or orphanages to read to children.