How to move forward on possible grooming for molestation ?

My 13-year-old niece is getting a lot of attention from a teacher. It’s making me a little uncomfortable. And I’m not entirely sure how to approach the situation.

- He corresponds with her a lot.
– She says he corresponds with a lot of other students as well.

- He emails her in the wee hours of the morning.
– She says its because he’s in the military and wakes up early.

- He invites her on special outings.
– She says it’s because he runs a teen program.

- He offers to pay for her.
– Her guardians can’t afford to pay for her.

- He asked to see a picture of her in a dress.
– In context, it was because she was joking to him about actually wearing a dress for her eighth grade graduation. She usually wears tomboy clothing.

- He jokes about her coming to live with him because her home life is so troubled.
– She says he’s just joking.

I’ve spoken to her about child molestation, grooming and how they’re usually an adult that you like and respect. I also told her to be aware if he is singling her out with special attention and presents. And not to get into any situation where she may be alone with him.

My question(s):
Am I being paranoid?
Is it possible that he may just be an okay guy and things may be misconstrued?
How can I be sure?
Can I trust my niece to be able to protect herself?
Or should we remove her from that situation?
If we remove her as a precaution, what can we do make sure nothing happens to the other kids in his program?
How can we be sure of his intentions without keeping her in harm’s way?
How can we be sure we’re not leveling unwarranted accusations?