Should I report my classmate?

I recently found out one of my classmates might be with minors and I don’t know where to go from here. 

I (17F) have a classmate (18F) who has admitted to having relations with two minors, and attempting to with one. I have heard from multiple different sources (even first hand) that my classmate has admitted to sending (and possibly receiving) nudes from a twelve year old boy, to having intercourse with a eighth grade boy (so most likely 14), and has tried pushing herself on a Freshman boy (so about 15). She herself has said these things with seemingly no remorse. 

After finding out I feel obligated to report this, especially because her plan in life is to work in early childhood education. However my moral issue is what if it’s not true. If this information is wrong I don’t wish to ruin the girls life, but I feel that if it is true she should be stopped. Especially due to her future career path and the kids she could possibly endanger. I’ve spoken to other classmates for advice and they have said to speak to a teacher. However my second issue is that I would prefer to remain completely anonymous. So while I agree I should report it I also feel nervous about becoming attached to the issue. 

If anyone has any advice on how to move forward I’d appreciate it. Whether it be on how to report it or whether I should. Thank you for reading.