I haven't really been showering or needing to clean up after my ride for the past few months, because of the cool weather. I do have access to a shower at work, though. I have found that wet wipes, deodorant, and a change of clothes have me covered for days it is warm enough to break a sweat.
Also, make sure that your wife has checked out tire pressure, seat position, etc. Those can all make it harder to pedal -> make her sweat more. How long is her commute?