I have an aunt who is gravely ill. She is my late father’s (may he rest in peace) sister. She has only one daughter and no sons, and her daughter has two daughters. While both of the grand-daughters are married, the husbands have both of their parents alive, thank G-d. Therefore I am the closest male relative. If the worst happens, I would like to say kaddish for her. Should I say it for one month or eleven months? Thank you.

You can say the kadish on her behalf for the full eleven months.