As you seem to appreciate, the company can't dismiss her by dint of her disability making her unable to do her job. Therefore they have an obligation to put measures in place which would allow her to use 'the system' - allowing her extra time to learn to use it, offering her adaptive software, a personal assistant, etc etc. - which, incidentally, they can probably get funding for.
If the lady still finds the job is unsuitable for her then it's up to her to say so, and to say why.