The fact is she was on your page, so yes, there Is no mistake on that, so yes she was looking at your page. Now while scrolling or something, she could have accidentally hit add friend, or hit add friend to see if you accepted to see more on your page. Then deleted you. So yea its snooping, and if she did it intentionally she should have left a message.

This I something to mention asap in session as it could affect your relationship. I would freak.