If your mother passed away and you were an authorized user on her credit card can the card company hold you liable for 100 percent of the balance?

Wrong, wrong, wrong..and they know it. This is a "scare" tactic that some less than ethical companies will try. It is also illegal. Authorized users ARE NOT!!!! responsible for paying debt incurred. (Joint account holders of course are a different matter entirely.) Send them a certified letter letting them know that as an informed consumer you know your rights. And one of those rights is to consider litigation of your own. Infliction of emotional distress is a good place to start. You lost your mother, and now they are counting on your loss to get their money..low, low, low. Do not let them bully you, "shove back"... hard!