Specify Open With application for stacks

I would start with a new user - if you felt it was easier to start there - you could always make one good back up, delete both users (keeping a third one for admin purposes) and migrate in your wife's account from the backup. You could make a new account for you and then copy in the files you want quite easily from the backup.

Most things you need are Documents, Music, Pictures so it's trivial to copy them back from a backup.

It's nicer to do this rather than go mucking among all the preference files unless you want to learn that end of things.

Issue solved: After the update the Recent Items selection in System Preferences>General was set to 0.