Does she have a cell phone? If she does, and the account is in your name, you can go online and open an account - and then you can see all the phone calls that have gone out and perhaps come in today. It would let you know the last time a call went out or came in.
She may also have GPS on her phone, and if it is on, she might be able to be tracked through it. Call the cell provider for more information and tell them you have filed a missing person report...
No she doesn't have a cell phone. She and her sister text-messaged the bill sky-high, and the account has been inactivated. You can bet that will be fixed tomorrow though!