Can you cash a check with OAO and my deceased mother's name on it?

Generally, you cannot cash a check made out to a deceased person, even with "OAO" (which typically stands for "on account of") written on it. You would need to go through the estate settlement process, which may involve presenting the check to the executor of your mother's estate or the probate court for appropriate handling. It's best to consult with a legal professional or your bank for guidance on the specific circumstances.