Your mother can add your daughter as a beneficiary to her will by either executing another will that revokes the prior will or by executing a codicil which is basically an amendment to the existing will. They both have to follow the same formalities required by law in order to be valid. If the will is simple, it is often easier to execute a new will so that you have everything in one document. If there are several codicils, it can be confusing to piece them all together. There are two...