Note that I am not licensed to practice in your state. This is not intended as legal advice. Please check with an attorney in your state.
You should contact an estate planning attorney immediately and tell them about the urgent situation. Ask them to come to the house to speak with your grandmother and to execute the will. Do not handwrite one yourself and have it notarized. There are many will formalities and you might find that the codicil (that's the legal term for your addendum) is not valid.
Go see a local estate planning attorney right away.
Thanks for your question. Since I am an attorney, I cannot ethically give you specific legal advice on your situation, since you are not my client, but I can only provide you with general information that you may find helpful.
Many attorneys, such as myself, routinely travel to their clients’ home or nursing home to address issues as you have described. Most states have now rejected holographic (hand-written) wills or codicils, and require the document to be executed with all of the formalities of the original Will. Rather than using a traveling notary, I would strongly suggest that your grandmother employ an attorney to redraft her “standard Will” and make the changes that she wants.
Perhaps it would be best for you to contact an attorney directly and provide him with more information to help assess the situation. This information is not intended to substitute for professional legal advice and does not create an attorney-client relationship. You should accept legal advice only from a licensed legal professional with whom you have an attorney-client relationship.
Best of luck to you,
Shawn C. Newman, Esq.
Attorney At Law
1881 NE 26th Street, Suite 212E
Wilton Manors, FL 33305
Licensed to practice law in New Jersey, Florida and the District of Columbia