If Casey had Amy's SSN and a few other pieces of info, she could easily set up a false ID.
Some years ago, a Los Angeles reporter was given $400 by his employer and told to try to obtain a false identity. Within 6 hours the guy had a drivers license, passport, and all sorts of documentation and he didn't spend all of the $400 given to him. There's places where someone can buy an identity. This was reported on to illustrate how people can come over the border from Mexico and obtain legal (false) documents.
I read an article about how you can do this so easily over the Internet!