She can’t prove owner ship. That’s why Apple won’t reset it for her.
When she bought it at Apple, she gave them an email, and she would have a record at Apple that she bought it. They would have all that information. Sounds like you bought an iPad that was stolen off Craigslist.
You can bring it to Mexico, they are real good at hacking into things at Eje Central, right next to the Tower of LatinoAmericana. It will cost about $40 and in 20 minutes you are good to go.