So I(30f) was visiting my sister(39f) she has a daughter(4f) who absolutely adores me. During my last visit, I noticed she was being particularly harsh with my niece, refusing to let her eat her chocolate bunny until after she ate lunch, going far as to tell her she would never get it when she got upset, only gave her the ear of the bunny even though she ate all her food and then refused to push her on the swing when she wouldn't take a family photo. She then went back over to mingle with our mother(74f) while my poor niece cried about being left alone. I gave her a hug and agreed to push her on the swing instead. Mom got a cute video of us having fun and bonding. However, my sister later pulled me aside and reprimanded me for undermining her parenting. I expressed that I felt she was being cruel to her daughter and she threw it in my face that I can't have any kids of my own because I'm trans so I will never understand how hard it is to be a mother. She also said that how she raised her daughter was not my place. This really hurt my feelings but mom said that I was really good with my niece which only seemed to anger my sister further. AITA or is sis just on a power trip?