By telling management, you're worried about the nice guy image.
By not telling, you feel that it's not fair to everyone.
The "rite" thing to do is to tell management, you might think.
However, life is not always rite, if not never.
To eat your cake and still have it too, you'll have to put on a
mask. Yes, be the bad guy but look like the opposite. Go to the
management with her. When they asked you why, act hesitant as if to
convey a message of reluctancy to tell on your team mate. When the
message gets through, tell them you forgot. There you have it.
