D.B.
If I'm reading you right, your sisters live close but you do not? So they are helping with the hands-on work but you are unable to do that?
There are some concrete things you can do that your mother may or may not agree to let you help with - but you can start the ball rolling. An obituary needs to be written. A funeral or memorial service needs to be planned if you will be doing that - either in a church, synagogue, funeral home or other location. That means an officiant needs to be contacted (minister?), music (e.g. hymns) may need to be chosen, meaningful spoken pieces might need to be chosen (poems, prayers), a eulogy needs to be written (that can be by the officiant, but often family members contribute their own memories. You (and perhaps your sisters) can begin doing your own words of memory, but you might be able to start some of the other organizing and phone calling. A casket needs to be chosen. If the funeral home dealt with things when your grandfather died and the same thing will be done with your grandmother's remains (burial or cremation, headstone purchase or engraving, etc.), they will be able to assist in dealing with the cemetery. Your mother (or someone else) will need copies of the death certificate for all kinds of reasons - getting a jump on something as simple as how many copies will be needed is very helpful. Life insurance policies, investment accounts, safety deposit boxes, pension accounts, etc. all require some sort of notification to transfer assets to the names of the heirs. If there is a family lawyer, that person can help too.
If you will expect flowers, you can arrange that when the time comes. If your custom is to do donations in someone's memory, then relevant charities need to be listed and addresses obtained (that often goes in the obit or on funeral home website condolence pages). If you want to set something up (at the local school or senior center or church, whatever is relevant to your grandmother), do that legwork now.
Arrangements need to be made to have someone in your grandmother's house as well as your mother's house during the funeral - this is when thieves often strike because they know no one is home. While you can't set the time & date obviously, you can start thinking of who you might ask to stay there (someone close enough that you trust, but not so close that they would be attending the funeral). If your custom would be to have people back to the house, you may need to arrange for some sort of catering or food platters. Again, you can't place orders yet of course but you can get some pricing done and find out about order times, lead times and menu options.
If you are close to your mother's siblings, perhaps you can start these discussions with them. At many funerals, there is a display board of photos or a laptop running a video of photos. - this can be at the funeral home or in the waiting area at a church, or at the house afterwards, If that is something your aunts and uncles would like, ask them to send you (or scan and email) photos for you to arrange.
It may seem maudlin to get going on these things, but it can a huge relief to the caregiver (your mother) as well as the siblings who are also at a distance and may be looking for ways to contribute as well as think about how they want to celebrate their mother's life.
This may actually be more helpful to your mother than talking to her about how she feels. The fact that she has so little time to talk right now may mean that she is overwhelmed with impending grief, but it may also mean she doesn't know how she will navigate the waters of details and arrangements (and perhaps trying to please her siblings who aren't around but want info from her).
This might not be what you have in mind. But honestly there is not much you can say right now while she is so frazzled. These very concrete takes take a lot out of the bereaved person especially one who carries the whole burden like your mother.
In my family, we talked openly about death, and all us kids were instructed on what to do "when the time comes" - we knew where papers were kept and what funeral home to use and what clergy member to use. As awkward as it might have seemed, it was absolutely invaluable in making the arrangements easier and in warding off any arguments among mourners.
Good luck - you're a good daughter for wanting to help your mother.
