If your mother purchased a life annuity policy where she was to receive equal payments under it presumably on a monthly basis until she passed away and she passed very soon after she acquired the annuity which then stopped payment upon her death, you can challenge the contract but most likely you will lose the contest for the following reasons:1. your mother entered into a contract with the annuity company and she (her estate) would be bound to its terms absent fraud by the company issuing the policy;2. the policy ended much sooner than you and your mother anticipated due to her passing;3. the annuity company took a risk that your mother would live much longer than she did;4. your mother took a risk that she would live a shorter time period and that is what happened.