This already exist. Tobii Eyemobile

I am a Neurologist and Neuroscience researcher. I work with fMRI (functional MRI), EEG and MEG( Magnetoencephalography) in my research and clinical practice. And I can tell you from experience, these methods are not practical for what you want to do which is daily continuous communication with your loved one. Your best solutions will be custom to your loved one, and most likely will be an eye tracker. I use these in my research with children and they are quite reliable.

  Look at Tobii (http://www.tobii.com/en/assistive-technology/global/disabilities/) for an idea of possible products. As part of her recovery, her MD's will have her evaluated by a speech/communication specialist and they will talk to you about many different solutions, including blink boards and eye trackers. But solutions vary, I have one patient that learned Morse code, because it was free and faster than a blink board.

  In any case,seek real expert opinions from people who's credentials you can vet, not people on the internet. This is really the only way to see which solution is best for you.

I am a physician scientist that does imaging work in the medical industry. As such I use higher level mathematics ( Tensor equations, Convolutions, Integral Transforms etc) daily. The key to programming in higher level math, is to solve your problem in such a way that it can be approximated using numerical analysis algorithms or linear algebra. To do this you need to understand your problem and be able to solve it on paper first, so that you know the limitations of your solution and can correct it accordingly. No one will pay for a piece of software that gives the wrong answer 1 out of 100 times.