J.K.
My son is the same way but he just gets up and walks away. He's 14 months. I just chalked it up to "not wanting his diaper changed" for whatever reason. I keep thinking that I just want to potty train him and be done with diapers for good. =) If she's healthy and has no rash, then she probably is just mad about having a diaper change. This might be motivation for her to potty train. My boys potty trained right around age two. My girls were older. =) Good luck!!