Important first step:
I think you will need to "sign out" of iCloud, iTunes, App Store, etc.
In other words, "de-authorize" the Mac (for you), so your wife can create new authorizations with her account.
Then, I think you could do this:
1. Create a new "temporary" account that will serve as an "intermediary" one. Give it a simple name and password.
MAKE SURE you give it administrative privileges.
This account will be used only "for the transfer" and can be deleted later on.
2. Now, log out of your regular account (after you have deauthorized everything)
3. Log INTO the temp account.
5. Now, DELETE your old account completely and remove anything you don't want to remain on that Mac. Now it's ready for your wife.
6. Next, while still logged into the temp account, create a NEW account with your wife's username and password (can be temporary password she can change herself later on).
7. Now, log out of the temp account and into your wife's new account. It's ready for her to sit down, get her accounts with iCloud, iTunes and the App Store set up, etc.
8. When she's all "set up", you can delete the temp account. Or... leave it in place if you ever need to sit down and do maintenance on it again...