Well, the guy at GNC is an idiot and an a--hole. That is not going to happen at all. He just wanted a sale. Sorry to hear that. I hate GNC. They're overpriced and then they tell you things like what you just said. From now on, buy your products online. There are a bunch of cheaper websites and you don't get mislead like that. Look at bodybuilding.com, vitacost.com, fitrx.com, allthewhey.com, etc.
I will disagree with InnerFight and say that what you eat is more like 75-80% of, and that inherently includes the mental part, because if you're winning the mental battle, you're eating the right foods. The rest is a combination of working hard and knowing what you're doing so that the hard work isn't wasted.
Your wife doesn't need to take protein. Ultimately, that is just a supplement and cannot replace whole food. It works great pre or post-workout because it's fast digesting and convenient, but in no way is it totally necessary. If she wants to take it to help her out, PWO is probably the best time.