AITK for not standing up for my cousin sister

Today me 19m was at my house and was joined by my cousin(mother's sister's daughter )19f staying for 2 days,today after eating dinner my mother asked her to sweep the ffloor, it was my masi who told my mom to ask her to sweep the floor and all because of some gender norms and shit so she can esstenaily practice, I know very dumb and backward and I agree, now my sister did not like it as as a guest she felt it was demeaning to her(she knew her mother asked for this) and then I said it was quite unfair and then my mother started to sweep the floor on her own,but my sister felt empathy for her and took the broom of her and did the sweeping herself and at night when we were alone she said that I should have said something to my mom in front of all of my family members which includes my father,both grandparents and my small sister,I said I had already had this conversation with my mom in private but mom justified this by saying her mom asked me(my mom) to do this, so AITK for not standing up for her