She getting the hang of it

Saphrin my oldest daughter is a very aggressive girl. She likes to lay on her sister and push her down. I tell her that she can't do that. It is very annoying because I fell like I'm telling her not to every 2 seconds not to beat up on her sister. WELL yesterday Saphrin was beating up on her sister like usual and Sophia slapped her right in the face. I was shock. I didn't think that she would every do that. I would never say this to them but it was nice for Sophia to show Saphrin that she is not going to take it. Saphrin just seems to do stuff to Sophia. Saphrin is becoming something else!! She is learning and is teaching her sister.