"I'm being a sister!"

So, the other day the girls were playing in the living room while I was cooking dinner. As usual, I hear Alina start to fuss, and go to check out the situation. Alina is on the other side of the room from Gabby, looking at her as if she had taken her favorite toy away. I asked Gabby, "are you being a mean big sister?" Gabby replies, "no mommy". So I ask, "well, are you being a nice big sister?" And her response was priceless, "No mommy, I'm being a sister!"