Last UKcat test this year is 7th Oct, there's one 23rd of Sept.....may be worth changing your test date - I think you can do that with no financial cost to yourself with 3 or 4 days notice. I'd suggest the later the better as she willget more study time.
My son got 732.5 Av. and that's a high score, most Unis are looking for 580+ but do interview at lower scores (the higher the score the more likely an interview is). some unis have a high cut off (around 680), see "Thestudentroom" website for lots of info, and the individual Uni websites. They all score in different ways, but the UKcat is much more important than you would think, it may "only" be 25%, or 15% of the application process but it's very important - as virtually every applicant has 5 or more A at Higher, Duke of Edinburgh, volunteering etc.
The Dyslexia is not necessarily a disadvantage in this test (as there is extra time), as it's all about pattern recognition - something we tend to be better at than "normal" people.
Edinburgh and St Andrews both have a harsh way of cutting down applicants - Standard Grade results are used (points removed for grades bellow "1"), so make sure Dyslexia is declared on her application if she got less than the perfect 8 x Grade 1, if it's declared the points won't be removed. Other Unis may do the same, but these are the ones I know about from 2010/11 application cycle.
Please PM me if you want any first hand hints re Aberdeen/Edinburgh/Dundee/Oxford, and 2nd hand hints re Glasgow/St Andrews.