according to the new disability discrimination act no university is allowed to give any person less of a chance at any course because of a disability of illness. It would be illegal for them to hold your friends illness against her when considering her application, though I do suggest she warn them before as telling them early will give them time to prepare any special arrangment she may need such as accomodation, extra lecture notes if she needs to miss class and extra time/comfortable seats/own room for her exams. Also most unis in the uk encourage student with these problems to apply for the Disabled Students Allowance which will provide money for equipment such as a new computer, a desk, a printer and a comfy seat, a dictaphone to record lectures if shes not feeling to good during, a palm assistant, software for referencing and mindmapping to help overcome the effects of meds when she's doing coursework and even in my case a full time helper for doing any practical parts of the course that I have difficulty with. The Uk is taking a positive approach to people with illnesses and disabilities going into higher education. Your friend should be very proud that she's taking such a big step and not letting her illness hold her back, I know from taking that step myself only last year what a big deal it is :-)
If you'd like any more info on your friends rights with uni admissions or the Disabled Students Allowance go to www.skill.org.uk
which is the national bureau for students with disabilities. They have all the infoo you could possibly want and were great to me when I fist started uni.
Good luck to your friend and I hope Ive helped
'Never judge a man till you've walked a mile in his shoes. After that, who cares? He's a mile away and you've got his shoes.'