@SummerDCs not sure re: atom. To be honest, the first stage is quite different to Atom / ISEB - paper-based, faster pace, focus on speed and accuracy in VR and non-VR. From our experience two year's ago, all the girls at my daughter's prep that got offers had also got offers from schools like PHS, KGS, G&L, LU, etc. but there were a couple with offers from those schools that did not get an offer from WHS - whether a bad day, different type of exam or something else is difficult to tell.
The school, as far as I know, does not provide scores - just whether people have proceeded or not. The scores from the first stage are carried over to the second one - a family friend did not get an offer and, on enquiring, was told that her DD's performance at second stage has been satisfactory but not strong enough to overcome that her round 1 score has been just enough to scrape through. Apparently, the school would usually tell people in WL in which third of the WL they are placed.
On summer adjustment, I do not think there is any. Looking at their intake at least in my DDs year, there are plenty of summer girls.
Given that the test is tomorrow, the only thing to do is for your DD to take it and be as relaxed as possible.