OK I have a serious legal question?

sorry for your loss. However, her authoriziation for you to use her card ended with her death. If you were signing her name after her death, it is fraud which is a crime, but you probably won't be charged in criminal court. However you will be held accountable to pay the total bill (or at very least for the amount of time you were solely responsible for the charges after she died). If you do not pay, they can take you to court to get a judgement against you and garnish paychecks/attach bank accounts.