Do i really need to take a digestive enzyme with my whey protein?

A very pushy (and condescending) saleswoman at gnc insisted that I was wasting my money by buying whey protein isolate and not taking a digestive enzyme because my body only absorbs something like 12% of any protein that I ingest. I did the math, which means I am only absorbing 2.4 grams of protein per 20 gram scoop. I don't know how much of this is BS and frankly I didn't like the way she approached the matter so I told her to piss off. She could be right for all I know. Is it necessary?