Get references and check them. Also, when you do this, find out not just what they think of them, but how they know them and how long. If they're in the US with a passport (not from the States), make sure they have a work Visa, otherwise you could get in trouble. Ask (and check) to see if they have any credentials (are they licensed to provide child care, are they CPR / First Aide cert.).
I don't know if this is something that you can do as an individual, but I know that I work with kids a lot through Scouts, my church, and with the schools, and they have a form from the Police that I fill out and sign, and they run a check on me to make sure I'm not some sex offender or anything. You could do that maybe, and if not, you can ask for her info and run a check on her through one of the internet background checks, to search for criminal records, etc.
at 8:35 AM on Dec. 25, 2009