Should i have hit her?

Recently, my best friend, Shayla's,father was diagnosed with Gallbladder cancer. It is untreatable and it has a 20% survival rate after 5 years. She became super sensitive at school when we started learning about the liver, bile, and of course, at the worst time imaginable, the gallbladder. Shayla stormed out.Me being the closest with her, asked my teacher if i could go out and help her. We were sitting outside of the clroom, just talking. The bell rang and she was just starting to get herself together. When this girl in my cl (known for being the rich, snobby, popular girl),Amy, came out and said to Shayla. "Shake it off, your embarring everyone around you, stop being a baby". Ive never punched anyone harder in my life. She broke her nose. Our parents used to be friends, surprisingly, and they said they wont press any charges. But i feel bad for what i did. People keep telling me "Good thing you set that b**** Amy in her place". Should i feel bad?