How to Switch to a New Apple ID (and Keep All Your Purchases)
Answer: There's an easy way to fix this using the Apple ID manager website. First, you'll need to change your account so that it uses your email address instead of your wife's. To do this, head over to appleid.apple.com in a web browser, click the Manage your Apple ID button, and sign in with your existing account.
Select the sidebar item labeled "Name, ID and Email Addresses," then select the Edit button next to the "Apple ID and Primary Email Address" field. Here, you will be able to change the primary email address that is associated with your Apple ID. When the changes are saved, you will be able to log back into all of your devices using this new email account.
Next, log out of appleid.apple.com, then head back to the main page of that site, where you'll see the option to "Create an Apple ID." Click it to go through the process required to set up a new Apple ID for your wife's account.
After everything has been completed, you will have your account with a new ID (and all of your saved items), plus a new, clean account that your wife can use on her devices.