Don't worry hon, concentrate on getting better + not worrying about it. Time for you to look after yourself before you immerse yourself in the stress of A-levels/ uni etc.
They won't dismiss you for it, especially if they can see what a strong person you are for not giving up despite what you're going through.
I disclosed information about my eating disorders to Nottingham with my application (they seemd quite insistant you tell them any health info, think its because they adapted the med school applications for the vets). They gave me an interview anyway and I'm still waiting to hear, but if they reject me it will be because my interview didn't go too well.
I'm not so worried about the exams in summer- happy with my results so far- but I'm screwed up with eating and know I need to sort that out as a priority. You can go back and do your A-levels any time, it's your health that matters most.
Take care + good luck,
Lucy xxx