Help?! I'm vegetarian and for dinner we're having fish and my mom is making me eat it?

We're also having squash casserole and salad which is what will be my main courses, but I refuse to eat the fish, but my mom will be extremely pissed and stressed out if i don't. I don't know exactly how to stand my ground. She says "Jesus ate fish" and that God put them on the earth for us to live. I don't know how to prove to her that I don't need fish for sustenance and that I can get the omega 3 and protein in other places. What should I do or say?