Libraries for gaze tracking with consumer hardware
Before I get all non-technical, check out Dasher. I used it for a long while on my handheld to type out long messages and it works like a charm. No hunting and pecking, just stare in the direction you want it to move (I used my stylus).
My grandfather was paralyzed from the eyes down from a stroke when I was just a baby. My grandmother worked out a way of talking to him using a piece of cardboard. She had three rows of letters: 1st half, 2nd half, and 3rd half (yes, third half. why, I don't know). The first half had letters A-H, second had I-Q, third had R-Z. She would hold the card up and go through his message letter-by-letter. He would blink when he wanted to choose a letter.
First, she would ask about which half: "First half? Second half?" etc. He would blink when she was on the right one. Then she would start reading off letters and he would blink when she got to the right one. She would right it down.
There was no "space", so you need to do some guess-work to determine some meanings.
Granted, this isn't as "techie" or cool as you might hope for, but it's a hell of a lot more personal than coldly blinking at a computer screen. Also, if the family is going to be using this with her, guess who's going to be touching the computer when you're gone? Not you, and not her. And families aren't great with computers.
Just a suggestion, and it only takes about five minutes to make, requires a sharpie and a pizza box, and only about a minute or two to explain. Sure, it's tedious, but it's also simple and effective.
Look at http://www.cogain.org/eyetrackers/low-cost-eye-trackers
there are free and open source offerings listed there, including one from codeproject (C++)
Windows 10, as of the Fall Creator's Update, has built-in support for Eye Control and the feature also includes a speech keyboard for communication.
The feature works with any of the supported eye tracking devices, one of which is a low cost but high quality consumer focused product, the Tobii Eye Tracker 4C.
For programmers Windows 10 exposes the Gaze APIs and there is also an open source gazeinteraction library that is part of the Windows Community Toolkit to make it very simple to create a UWP application that responds to your eyes.