Ask the expert: Dyslexia and reasonable adjustments

We have an employee, with less than 12 months' service, who was under-performing and making errors in typing and filing. We suspected dyslexia and she was sent for an assessment. The assessment came back as the employee having mild dyslexia and below average intelligence. It suggested a number of reasonable adjustments but we felt, because of the employee's low intelligence, that the adjustments wouldn't have an effect. We dismissed the employee without discussing the adjustments with the employee, or putting any of them in place. The employee is now saying they will go to an employment tribunal. Can we justify not putting in the reasonable adjustments on the grounds of her low intelligence?