said by ArizonaSteve:If they can't collect it from her then they will probably turn it over to collections and if they can't collect from her they will probably come after you if your name is also on the account. At least that's what they would do here. You may need to get a lawyer and sue her to get the money back. Also, you better do some checking and find out what else she hasn't been paying like other bills and property taxes, etc.
Authorized users cannot be financially liable for the account. Only the account holder can be held liable.