Ask you wife to slow down? When my wife rides with me (rarely), I let her set the pace (I am faster than her), she leads, and she tells us when to stop for breaks.

Until your engine gets stronger, I would politely suggest you reverse the above. You lead, set the pace, etc...

Is she out riding with you for your company, or to do her own thing and ride for a work-out? Teach her to practice spinning and have her use lower gears, get a dog, and trailer (or kid) and have her do the pulling.

Lastly, get some sort of tandem - DF, recumbent, or trike?