Potty training help!!

So I am a nanny to a 3 year old who has been peepee potty trained for quite some time now and just started going poopoo in the potty. The reason she goes poopoo now is because she gets a prize every time. I don't mean like a sticker or a cheap .50 toy, these are nice toys. She gets one even if she only goes a tiny bit and she's smart and has learned this. So now she goes 3-4 times every day!! I never thought I'd say this but how can I discourage her from going poopoo so many times a day!?