Maybe home is not an option right now... What do the doctors say about travel, day trips, etc.
MS is an awful disease. My grandmother has it and underneath their "condition" is someone who wants to do the things and see the things that they once could, and it is terribly unfair that they CAN'T. My grandmother would HATE being in a nursing home... I mean, I think she would literally be kicking and screaming about it. To her a nursing home is where people go to die... and she has so much life left to live!
So, it is understandable that your grandmother wants to go home! If she cannot go there, what CAN she do? Even going to town for an hour, or taking a drive may do wonders for her! Even the nicest of nursing homes feel like decorated hospitals, including food that isn't "quite" gourmet... and most of the residents spend most of their days sitting in a room... just waiting. People need engaging experiences and things to do (heck even washing dishes has its value...) Since she can't go out and do things by herself... try to take her out frequently. Caring for someone with MS is a lot of work... but for a short period of time a regular person with a little "training" can do it. So try to pull together your family (with the help of doctors and nurses) and figure out a way where she can spend this lucid time being a real "human" again... going places and doing things!
And as for her question... have your mom and her schedule a meeting with her doctors to discuss the situation. She may be confused... but she is still HER underneath the MS... Even an answer like "maybe in a month or two..." gives her some light at the end of the tunnel! I mean, how would you (or me or anyone) take it if you were stuck in her situation and you said, "can I go home?" and the answer was "No, you'll never be going home again..." Instead... have hope for her! Even though I don't want to sound naive... never underestimate the strength of the human spirit. She needs your family to see her as a person with a future, full of possibilities... even if it is hard to do!
Good Luck!
-M.