Unfortunately her preparations are now going to be relying on you. I don't want that to sound mean or harsh, I'm very sorry for what she and your family are going through. A lot of the prep's for young children will apply. Having lists of meds, Dr's, contact information, and important paperwork safely stored else where or ready to go. Important paper work for the elderly should also include wills, power of attorney, medical power of attorney, medical and life insurance information.
If she doesn't live with you granny cams will help. Even if she lives with you, cameras might be a good thing. If she becomes injured and you don't see it happen, when you ask and she says I don't know. Now you can look back and see what happened. Even if it is to just find her glasses. Check lists attached to places where she will see them may help. Using medication organizers. Keeping her in familiar surroundings can help keep her grounded and in a routine.
The reason I mentioned the camera's is a good friend of mine went through this with her mom. Having the cameras in the house allowed the mom to live in the "family" home for several years longer that she would have been able to otherwise. Of course you may also learn that her favorite breakfast is beer and ice cream. My friend stopped by several times a week to stock food and provisions for her mom so there was only a few bottles of beer at any given time. Along with that she could also monitor whether or not mom took her medications, if she didn't a phone call to gently remind her to do so.
You will need something to keep her occupied if you have to go somewhere or bug out. If you think it's bad when the kid's are asking "are we there yet". It's worse when mom asks for the tenth time "where are we going". This could be something as simple as asking something about the past she does remember, a favorite trip or vacation, something you did when you were little, a favorite movie, or old family pictures stored on a portable player. This will be something that you have to figure out and it will change as time goes on. A friend of mine confessed to me once that he felt horrible about whet he did to his mom who's short term memory loss now spanned several years. Several times a week he would loudly say "HAPPY BIRTHDAY MOM" and then hand her a stack of birthday cards from years gone by and she would dutifully read each on out loud, fold the card back up, place it on the bottom of the stack, read the next one, and roll all the way through the stack. When she came back to the first one she didn't remember that she had already read it, she could do this for hours. He said that this was the only thing that made her very happy and kept her engaged for several hours.
Aging parents can be a very difficult thing to deal with. For myself, I've had to start locking up the ladders so that they are not accessible. My 80+ year old mom thinks that it's still OK to get on the roof to sweep the leaves. Yes, it's good that she is still active but it's always in the back of my mind about what is she going to do next time.
I hope some of this has been helpful and not just depressing. I know this will require a great deal of time and patience for you and your family.