Someone found out that their grandmother, who passed away 7 years ago, didn’t have anyone that said kaddish for her for the year after her passing. Is there any inyun now to say kaddish for a year (starting on her yarhzeit which is coming up soon.) Is there any source or this or someone that speaks about whether the practice is to say for a year or not in such a case?
Yes, there is still an inyan and a benefit to the neshoma when kaddish is said, even if it was only said after the year of mourning is finished. The idea of saying kaddish for the first year or 11months is because it is brought that when a child says kaddish for the parent during the first 11 months it helps the soul of the departed from the tribulations of gehinnom. There reason for the minhag to say kaddish for 11 months while aveilus lasts for 12, is because it says that the pains of gehinnom for a rasha last for 12 months, (and sometimes even longer) and the child does not want it to appear that his parent is a rasha, therefore the minhag is to say kaddish for only 11 months. Therefore if the kaddish is only being started after the year, the idea of specifically 11 months will not apply.
As a side point it is important to remember, that any torah learning especially mishnayos is very helpful to the neshoma, at any point, even after the year is over.
Livush O:CH 133-2, Kallah Rabosi 2-9 and Tana D’bay Eliyahi Zuta 17-30 relates the story of a tanna who met a person who was a big rasha after his death, and he wanted to help him. He went to the man’s town, and found that his wife was pregnant, he waited until she gave birth, gave the child a bris and when he grew up a little, he taught him chumash etc. and brought him to shul to praise Hashem. It says there that when the child praised Hashem (kaddish) the father was taken out of gehinnom, and when the child learned torah the father was taught that in heaven. We see from this story that although the child didn’t say kaddish until a number of years after his father died, that it still helped him.