You will need to contact the Medicaid agency. Once your mother sells the house, she will be ineligible for benefits until the proceeds have been spent down. The Medicaid agency may or may not also have a claim for reimbursement from the proceeds. That differs from state to state.
We recommend that you consult with a local elder law attorney who will be able to advise you on how the rules are applied in your state and whether there may be strategies available to save some of the sale proceeds.