Not a problem at all. I'm 6'3", and my better half is 5'0". Well, to be honest, we now have a custom frame (seat tubes are 48 and 61cm), but even if you don't want to put your money now on a custom frame, it should not be a problem. Take a frame with a rear seat tube short enough for missus, and the longest possible rear top tube. Chances are that the front seat/top tubes will be much shorter than on your solo, but with an extra long stem and seatpost, it should do the job.