Rexy is not a true hero. She doesn't help the heroes willingly or out of redemption. She does so purely out of instinct and still would have gladly eaten the heroes had the bad dinosaurs not been in the way. And no that doesn't make her an anti-hero.
Look, I will stop messaging you if you agree with my proposal I made of Shrek 5 and Puss in Boots 2? Alright? You do that for me, like you did to Ice Age 6 and Madagascar 4, and I live you alone. You can even block me if you want. It won't make any difference.