Fraud Fraud, Embezzlement, Bad Checks

My husband had a dog when I first met him, after a while we moved in together and he gave his dog to his mother which was in 2006. In Dec. 2007 we stopped having anything to do with his family including his mother and we have not spoken to them since. In Oct. 2008 this dog dies, a couple days ago we get a letter from a bill collector saying that we owe the vet $300 so I called them today to see why and they said for the dog that died in 2008. Well his mother brought this dog to the vet and put it on my husbands account even though the dog is no longer ours and she has them send the bills to her house so we know nothing about this until we get a letter from collections. I spoke with an officer briefly and he told me that she commited fraud by using my husbands account. My question is, does anyone know what kind of trouble she is going to get into if any and are we going to have to pay this?