It may just be that playfelt as she is a very "needy" child in that sense. It may also be exploration as today I let them play at the water table when we were outside and everyone got wet. So, when I brought them inside I stripped them all down to their diapers and let them run around for a few minutes before putting new clothes on them...and guess what she was doing... pinching herself. I think it may be that since its warmer more skin is exposed and she likes to play with it. If the mom brings it up again I will say something to her, as she didn't say anything at pick up.