2 nd Apple ID ?
How can I get a second Apple ID for my wife ?
iPhone 4S, iOS 6
You can create an account via this page : http://appleid.apple.com
Or you can create one on a computer's iTunes - if you are currently logged into an account then log out of via the Store > Sign Out menu option, and you should then get a Store > Create Apple ID option.
Creating an account : http://support.apple.com/kb/HT2731
Creating an account without giving credit card details : http://support.apple.com/kb/HT2534
All content that is downloaded from the store will be tied to the account that downloaded it, so if your wife wants to use any of your downloads then your account will need to be authorised on the computer's iTunes that she syncs to.