Someone is unfriended on my fb. but I dont remember she unfriended me or I unfriended her. Can I determine it?

FACEBOOK is an impersonal contact forum. Of Little value if you never meet face to face.
So back burner the subject, either way it has no real meaning to either of your or hers life.

The World will still turn, and sun will still come up in the morning.

You cant Either you have to Remember if you did it or not or it has to be her there is no way to find out which one of you Did it Facebook does not tell you who Unfriended who

thereis no way to know