How to unlink an iPhone 5c from the previous owners iTunes account?

I bought a 5c from kijiji three months ago. I loved the phone and it worked great while it was still in the sellers hand. I brought it home and did a factory reset and found out that it was linked to the ladies iTunes account.

Here's the best part. She has vanished. I have not been able to track her down. Not thru Kijiji nor at the Gmail address from the add.

Is there a way to unlink a phone that is linked to an iTunes account?
And after three months with this phone it is still not on the black list. So I don't think she was meaning to rip me off.

Do you have anything on the phone right now like pictures that you want to keep? If so you will want to backup with iTunes on your computer. To do this plug it into the computer with iTunes installed and a screen will come up with the iPhone. Click backup but make sure its selected to backup to the computer, not iCloud. After doing this, you will want to unplug the phone and turn it off. After its off, plug it into the computer, and hold the power and home button down until a screen with a USB cable and an iTunes logo shows up on your phone. It might take a minute for the computer to recognize the phone but once it does you will want to restore it. This will reset the phone to the out of box state. Once the restore process is done it will ask you if you want to set it up as a new phone or from a backup. Select backup and it will restore your content. Only choose this if you backed up the phone before. If you didn't, set it up as a new iPhone. Best wishes.