There's a few ways you can go about it. You have to really decide which is best for you and her:
- Go to Settings>iTunes and App Store>Tap on the Apple ID and sign out of yours. She can then create her own on the device or just through iTunes and then login from there.
- Wipe the device and set it up as a new one through iTunes, while creating a new Apple ID for her.
In either case, there is a few things to keep in mind. If you wipe the device, any purchased/download apps won't transfer over. You'll need to purchase/download them again using her newly created ID. If however, you simply log out and then just login to her account.. the apps will remain but you most likely won't be able to update them as they're not really associated with her ID at that point. They're just kind of there from another account and while they'll mostly all still work often times, it'll nag you about that via various authentication errors and such.