A phone call? Who did the caller claim to be? Has she received anything in the mail regarding this incident. You will soon be hearing from qualified counsel licensed in IL. Your GF needs to talk with an attorney who can gather the necessary facts. Given her career goals she needs to get in front of this. it sounds like a variation on the civil demand scam, but I can't be sure without answers to questions. Neither you nor she should post any additional information about the incident on the Internet.
Your girlfriend needs to retain an attorney to write a letter denying any liability. Paying this civil demand is unnecessary, especially when your girlfriend was not held or charged with retail theft. Please read: