maybe food smell.
maybe they think you have a treat in your fingers.
I have one that at refrigerator I give him live mealworms, after he is finished eating one I get him another, if I dont go fast enough he will give me a small bite on the arm he is sitting on. like he is saying hurry up with the next one.
My wife's glider will sometimes give me a little nip during playtime, don't know why.
the gliders like to give bare toes a nip, I guess feet smell tasty.
None of these are hard blood bites, just enough to get my attention and annoy me.
I would think, she is testing you for some reason. get a treat, smell something good so give it a nip. something like that.