Having not worked in legal services personally, i can't directly quote you on it but the equality act does allow for reasonable adjustments in the workplace and for you to sue employers under that act if they don't provide them. So i wouldn't go saying that to people unless you as a disabled person could say that or as someone in legal services, who had had that happen to them. As a dyslexic person myself, i have had many (and i m not saying you are one, ignorant users on tsr) tell me employers wont care or won't hire me or give my reasonable adjustments but so far I have had no evidence to say that they aren't willing to do so for me.
She could certainly sue her university and take them to the education ombudsman if they weren't providing adjustment for her (if she has post 16 evidence, she won't need a reassessment, otherwise she will be but from my experience universities are more flexible than gcse/a level exam boards) .
Although i agree with the advice of doing some practice papers to make the decision, advising someone not to use it out of fear, just makes some almost feel more ashamed to ask for help when an inclusive society is what the allowance of extra time should promote.
Sorry, i realize that this might come across as an attack on your opinion, i dont mean it to be, but i dont want fellow disabled students living in fear of disclosing their diagnosis.