Until someone who has the experience you mentioned, and knows what they are talking about, comes along, I would guess that one way it might work would be to clone the internal uSD card in your wife's Touch. I also would expect that the "Account" page in "Settings" would be a way to "Sign out" of any account on the device and when you setup the Canadian bought device in Brazil with your wife's account data it should be what you are asking for.
Also, depending on what's wrong with the wife's Touch, a clone of your Canadian bought device's internal uSD card might fix that one as well.
https://www.mobileread.com/forums/sho...d.php?t=209122
Has the tools and instructions for doing the cloning.
Luck;
ken