Dyslexia doesn't negate your ability to use the English Language really well (as rebecca's question will show). Perhaps Rebecca got someone to type this for her whilst she dictated it, or spent a really long time with a spell checker, etc!!! I know someone with dyslexia who managed to do exceedingly well and achieved A grades in English at school.
However, having been closely associated with a dyslexic child it dents their confidence and self esteem to a great degree. A new job might have flustered and worried Rebecca which is why she failed.
Most dyslexics who do well in their working life have the full backing of their family and learn coping strategies. In fact many dyslexics are brilliant at lateral thinking. It is therefore possible for people with dyslexia to hide it and if schools or parents are not on the ball, children can go out into the working world without it ever being picked up.
Rebecca, I agree with Octavious that you would do well to seek help from someone who really understands the problem. Try looking up Dislexia help online, or speak to your GP or optometrist.