Why does my cat keep barfing?

My 10-year-old cat, Fluffy, keeps barfing up her food (Meow Mix Original Choice Dry food). We haven't made any changes in her diet, and also sometimes I see a splotch of blood in her feces. Please help! I just hate to hear her I'm-going-to-barf meow.This time she scratched me! (but I treated the wound.)