humor... compassion.. directness.

"Grandmother, you are telling me to eat?!?"

"Grandmother, thank you for caring about me so much. You've taught me when and what to eat... So now you don't have to worry about that anymore!"

"Grandmother, I love you and I'm so lucky to have you and your love. Sometimes I feel a little annoyed when you tell me what to eat, when to eat (or whatever). Could you trust me to do those things on my own now?"

You and your grandmother sound very loving and sweet.