The other day on the phone she finally got "Grandma" really really clear. She's at that stage where she babbles and then in the middle of it all, I hear something I can recognize. I'm sure the kids understand her most of the time since they talk to her 24/7 (or thereabouts).
Hearing her say "Grandma" was one of those moments. Kind of like the first time my son hugged me in the night and said "I love you".