first of all it sounds like your grandma, still has all her faculties at the present time. This sounds like the first stage, whch is severe depression. I took care of my mom when she had alzheimers and i took care of her till the end. The only thing different with my mom is she lost her memory it happened slowly but i am kind of glad she did it made it easier on her yet harder on us.when they loose the memory they don't relize what is happening. anyway they don't all lose it like my mom did.
The only thing i can really suggest maybe is try to think of things she used to love to do.possibly being with the grandchildren.taking walks in the park i don't know if she ever liked puzzles like the word searches are the easiest. from what i have learned in my medical profession is if you try to get her to do things that require using the brain it slows down the progression of the alzheimers also medication is she on any?
well i hope this will help some. as for lying in bed it is normal depression wise but it is an absolute must to see if you can get her out of the bed because it cause more trouble bed sores and the brain will disintegrate quicker.Also talk to your doctor just to make sure that i am right, like i have said to other people i am not a doctor nor am i a professional i am just stating facts from past experiences. which is what made me go into the profession i am in. a med tech and cna.