How do I get my grandmother to let me help her when she is such a proud women?

I have lasted a year, and now she's almost completely blind. She's been in her home for over 70 years, and I thought I could do this, but she makes it soooooo hard. She's childish, and I have a 3 year old son who adores her, but doesn't understand that sometimes she enjoys him around and sometime she slams a door in his face. NoOne else in my family will help me, except my mother (once or twice a month for a couple of hours)and god bless her for that. I DO appreciate it! But, I feel like my little boy is suffering sometimes because of this situation, and i love my grandma so very much. and I know it is only going to get worse. SOMETIMES she won't even eat because i bought the food. I planted her an acre of garden, and she won't eat anything out of it, she seems to resent it, i get that part, but she tells people i don't fix her a bite to eat, and that is so wrong, and it hurts so much. and then she's so sweet and apologizes and says I'm just old and cranky honey. I need help!