How's the grandma still alive and perfectly fine?

I don't think she moved bcs yk how old ppl are. And ion think that the monsters discovered her bcs of how quiet she was

I mean she still need to eat, move around too. She might have sleep a lot tho. But doesn't she feel the need to go outside? Idk? During the apocalypse- Oh god, I should shut up and be glad she's fine (￣ε(#￣)Σ

It's alright to be curious! My guess would be that bcs of her age, she could have dementia or smth, bcs older ppl tend to forget things easily. Also, i think the reason why he had to carry her besides her age, is bcs she felt numb thus making it hard for her to move that easily.