How Would You Tell Your Friend That?

There is this Girl in my hostel, she has a mouth odour, though i don't know if she is aware of it and i'm not the only one that has noticed it as some other person's in the hostel and outside do.
But the problem now is How do we tell her she has a mouth odour?
I  would have really love to tell so she can do something about it.
Please advice.