Posting for a friend: My mother passed in the US on 17th Av at 03:00am. She was brought to Israel for burial a few days after. I started saying kaddish at mincha of the 20th of Av, after my mothers kevura in Israel. When would be the last kaddish of the 11 months be?

ב"ה Shalom, My condolences to your friend. Based on the information provided, Avelut began on the 20th of Av and therefore Kaddish was said only then. Following the Ashkenazi custom, the last day of Kaddish is the 19th of Tammuz, Tuesday, two day from now, June 29. Besorot tovot