Sheva has no actual purpose, and when you look into Sheva as a character, you can really see this. Her backstory is very minimal (parents got killed by Umbrella somehow, and it's her people dying), her personality is almost non existant and she just happened to be thrown in to calm down the racist claims, which is one of the worst aspects of her. Then you have the AI (Chris's AI is also bad from videos I saw, honestly) which is truly bad - it kills itself and hurts you, acts up, and everything. But co-op removes nearly all horror/tension from RE.
Rose sucks too, but we have the MGS thread for going on about her
Sheva's character development is non existent. That's no reason to hate her but she got me killed too many times. At least Ashley hides behind you if you are shooting
I know the AI is the real problem but I never played as her so she gets all the blame