My son is doing the same with his MBP (he also just moved away and started college).
Like your niece, he wanted his own account. Apple does not make it easy or potentially cheap. You essentially start from zero with apps and music; if you aren't careful you can wipe out photos, contacts, etc. In researching the best way, I was amazed how many divorce settlements include keeping the iTunes account. Apple has ignored this since the start.
Itunes purchased Music -- rip it to get rid of DRM, then copy it back to new iTunes account
Apps - get out the credit card
Here is what I found for contacts, etc.....
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First, you’re going to need a Gmail account, which will make moving contacts to any platform simple. If you don’t have a Gmail account, quickly sign-up for one on Gmail’s homepage. Before you even touch your new Android phone, plug your old iPhone into your computer and open iTunes. Then, find the Info tab on the menu bar at the top of the window. In the drop-down menu next to the “Sync Contacts With” box, select Google Contacts, and then type in your Gmail account information in the window which appears. This allows Gmail and Apple to update your contacts so all of the names, numbers, and emails from your phone’s contacts are now stored in your Google account.
Note: For those of you switching from Android to iPhone, simply plug in your primary phone, navigate to the Contacts page, click the Menu button, and select “Merge with Google.” Now all your phone contacts have ported over to your Gmail account.
We suggest you then log into Gmail to modify those contacts before syncing them with your new phone. If you had a Gmail account prior to this process, you will notice your contacts list is now much larger and likely has some duplicates. If you see duplicate contacts, you may need to spend some time deleting or modifying them. It’s best to do this manually, but Google does have a “merge contacts” tool which attempts to do the same thing, it’s just not always accurate.
If you want to give it a try, got to the “more” button with the downward arrow, located near the upper-left portion of the window while on your Gmail contacts page. The drop-down menu gives you the option to “find and merge duplicates.” Selecting this option tells Google to automatically search your contacts for duplicates.
Transferring Contacts
Now that you have your contacts in Gmail organized exactly how you want them, it’s time to put them on your phone. If you haven’t powered up your new phone yet, this process will be easy. When you first boot up your new phone it asks if you want to sync your phone to a Google account. Simply enter in your Gmail information and your phone automatically imports all the contacts from your account. We told you it was easy.
However, if you couldn’t wait and already turned on your phone, but didn’t sync it with a Google account, head to the settings menu. There, you want to select the “Accounts & Sync” option which shows you every account synced with your phone. At the bottom of the page you will see a button labeled “Add Account,” where you’ll now enter your Gmail login. Once you select your Google account, it will not only sync all your contacts to your phone, but it also automatically sets up your email too.
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