so, you were never a saleswoman?
i've known people that do all the sales pyramid stuff and go nowhere. the issue is usually they want the end result (or, the "free" products) but don't really believe in it or care to do the work.
The good news is any fitness is good and jumping in the pool, even at the shallow end, is a good sign.
your job is 100% encouragement, light touch and keep her talking about it.
worst case, you get a hotter wife that needs to borrow some money from you.