Going back to the first post in the thread and re-reading it, I'm going to assume a couple things I didn't in my first response.
1. You're both going to ride primarily on pavement (tarmac).
2. The wheels/rims are the same size on both bikes.

Given that, putting a set of Specialized All Condition Sport tires on her bike is a "cheap, easy fix" - especially as you've already confirmed that they seem to make the ride easier for both of you. Stick with the narrower width range (23-28) IF you're not going to carry any medium-heavy loads like for touring.

OTOH, you will likely find that after a couple weeks of riding, you really won't notice as much difference riding either bike "unloaded" as your muscles should have adapted and gotten stronger, your pedaling technique will have improved, and even small improvements in your basic bike handling skillls will make things llike starting from a dead stop easier. So, you could use the "more difficult" tires yourself and just live with what you have as you adapt - or temporarily put off making a decision/change for a couple weeks and see if what I said here is applicable.