My cat coughed up poop? Or hairballs?

I didnt see her cough it up but i saw a long string coming from her mouth and at the end of it was some poop. Or at least it smelld like poop. She threw up like an hr before tht I think it might be cuz she ate her food too fast cuz some of the kibbles werent chewed all the way. She's a little bit more skinny on the sides as well. My sister is taking her dog to the vet in a week and ima go with her to get a check up my cat. But can they tell if there's soemthing wrong with her insides? pls help me thanx