How do you factory restore an iPhone 6?

My younger cousin accidentally disabled my aunts phone by entering the wrong passcode too many times. It now says "Connect to iTunes". The laptop she had synced with previously, is no longer working, and she can't remember her iTunes password. The email address she used for her iTunes needs to be verified using her old phone number which is also out of use. Is there any way she can factory reset it without needing these details? She still has the receipt of the phone, so proving she owns it is no problem, but she's short of cash so bringing it to a store will be the last option.

Put the phone in recovery mode by holding the home and volume up buttons while powering it on, then plug it into a computer with iTunes installed. ITunes will ask if you would like to update or restore the phone. Choose "Restore" and it will erase the phone and restore it to factory settings.