I am 68, and I have had CHF for the last 10 years, along with the a-fib, and it gradually gets worse each year. Things that I was able to do last year, are either harder or impossible this year.
Yet, I am determined to be as active as I am capable of, so I go out and work in my yard and garden, even if it is only for 10 minutes, and then I have to rest. Trying to use the weedeater totally wears me out, and this year, by husband often has to start it for me , because I can no longer pull the cord enough times to start it before I am too tired.
I imagine that your grandmother is going through a similar change in her life, and she can only do what she can do. I used to love to walk, and often took my dog and walked for 2-3 miles a nite. Now, I need the shopping cart to hang on to, just to get from the car to the grocery store. Not enough air.
I have gained weight, and am trying to diet and eat healthy to lose it, but when exercise is hard or impossible, so is losing weight.
I think, just let your grandmother know you love her, and give her as much support as you can in dealing with this illness.