Something I cannot possibly stress enough is that
this is something your mentors should be dealing with, not another student.
You've mentioned reporting it to your mentor, that was the way to go.
It's now up to the adults on your team to get to the root of the issue via discussion with the students and create a solution that works well for the team as a whole. It is not your job anymore, especially as an equally new member of the team.
I'm saying this as a student who was the only leader on her team for the first three years of its existence. Not fun - we needed adults for sure. It
should not have been my responsibility to sort out personal things between other students - but we didn't have any mentors, at all - so it was. It put a great deal of strain on my personal friendships, and while I certainly learned a lot about conflict resolution and how to approach situations like this, I definitely don't recommend it for any student. There may also be forces at play in these situations that it's not appropriate for another high school student to be privy to.
Let the adults handle it now. As a student, your job is to help continue a culture of acceptance, learning, friendship, and mutual respect for each other. Keep on doing that.
