An important statement
A contract is not terminated by death unless it says so within the contract.
What that means is your mothers estate is still bound by the contract unless the terms release it. That is where Quincy’s suggestion to read the contract comes into play.
If the contract does not terminate at the death of the lessee/purchaser, it remains in force. The estate would then become liable for fulfilling the terms of the contract. Whether there is an option to buy out the contract for less than full price or terminate the contract without further obligation will be determined by what is in the contract.
Whether the mortgage is in your name or not is irrelevent.
A side note: you are not obligated to transfer the mortgage into your name if you do not wish to. The garn st germane act prevents the lender from calling the note due if the property is inherited by a child of the debtor. While you can simply continue payments on the existing mortgage loan, it will not reflect in your credit history as it is not in your name. If you fail to make payments on the mortgage, their security interest in the home will allow them to repossess the home just as if your mother was still alive and failed to make payments.