As already mentioned, the key to her enjoying the sport is to do it on her terms. My wife is a pretty strong rider who enjoys riding, but only when it's on her terms. Therefore, if she wants to avoid hills, we avoid them. If she wants to stop for lunch half-way thru the ride, that's what we do.
Interestingly, for her, riding is a social activity, so going out with friends for a "spin" that might include a lunch stop is much more fun than going on an organized or training ride.
I've got lots of other opportunities to ride on my terms, so if accepting her terms will keep her riding with me, I come out a winner both ways!