Conversations with Avery again:
Let me set the scene, Brennyn is at the bottom of the stairs crying. I ran into the room to see what's wrong.
"Arey hurt Bwennyn". Avery is trying to look busy reading her book.
"Avery, I said you would go to your room if you hurt your sister again".
"no mom, you said I would go to my room if I hit Brennyn. I stepped on her stomach I didn't hit her".

I did ask why she hurt her sister and her response was "because Mom, I'm still a little bit jealous".
That's the new excuse. Oh, and be sure that when you are talking about your children they hear everything you say (for example when you mention a little bit about sibling jealousy).