How about a special girls night out as an incentive? Maybe a spa day or shopping and a nice restaurant or movie, or even a short trip?
My husband and I rode with my 15 year old son to his girlfirend's house, 10 miles, and it did him in. The husband and I continued on for 30 more miles. I don't know if I should be happy or sad that 2 "closer to 50 than 40" year olds are more fit than the kid.