Is this considered abuse between kids, how can I handle this situation?

I have always talked to my kids about people touching them inappropriately since they were little, and just recently my daughter talked to me about what she went through when she was much younger. I’ve been through this so I definitely know what I should do if someone ever touched my kids but I never thought that It would be by her own girl cousin who is 3 years older than her. She doesn’t exactly remember how old she was or how old her cousin was at the time but she had a sleep over at my sisters house maybe 4 times when she was little and my sister would always be home with them so I never worried. My daughter told me that her cousin touched her thighs and chest and then tried kissing her in the mouth. My daughter is 14 now and her cousin is 17 she said the only thing she remembers is that she had just graduated but she’s not sure if she graduated from middle school or elementary when it happened. I wanted to talk to my sister about this but my daughter doesn’t want her to know and idk how I would feel on thanksgiving dinner, I mean I know she was young maybe she was just curious? But it’s affecting my daughter because she says now she thinks she might be attracted to girls but she’s not sure. She’s going to see a therapist soon, I just don’t know how to handle this situation with my family 🙁 should I even mention anything?