I'm in a similar situation. My wife and I got a 7.1 and a 7.3fx at the start of July. She still averages 12-13 mph whereas I've progressed from 14mph to 17mph for 20 mile rides in the same timeframe.

The difference is in training. She rides maybe 20-30 miles a week. I ride 2 weekdays and both weekend days. The weekdays are hard 20-30 mile rides, as hard as I can possibly go. That may include intervals or hills, or maybe just a mile or two of trying to maintain 21mph (and then of course a few minutes of slow recovery riding). Either way if my legs aren't burning, I feel like I'm slacking on those weekday rides.

Then on the weekends I go for distance. That started with 40 mile rides, and has moved to 65-70 mile rides. I'm not as concerned about pace on these, altho I still try to keep going as fast as seems reasonable given the distance.

With the varied training, it seems that progress is coming nicely for me. I'm sure its not the optimal training plan, but the time requirements are light on the weekdays and heavy on the weekends, which is what I need given the constraints of working life. Maybe it could work for you too.