Don’t give up, Tom! The weather will be better. The negative result gives experience, probably something of your gear wasn’t suitable. Check it better, correct and go again. It is good that she wants to make a tour next year. Chose the temperature conditions/season more carefully, eliminate hilly areas as possible, shorten daily distances, more days to rest on the route and it will be fine.
It is difficult to get my wife more fitted. I use a velo-trainer at home just to be fitted, not to increase the average speed on tours, this is not too important. I do it like you, just have read your website. The conditions for cycling is poor in our town, heavy traffic is everywhere. But … such working out is boring for my wife and it is nothing to do. I think the only good idea is to go to suburb on weekend bike tours, because one must be fitted for loaded touring as well as for active life in general.
I hope to read about your positive experience on future bike tours and wish you to enjoy cycling with your partner.
Alex.