Don't worry too much about the change of date-It's the same year group taking the exam so the same amount of kids. In your favour the rolls are falling generally for secondary schools on the Wirral and many are laying on buses from south Wirral, Chester and North Wales in an attempt to attact pupils from those catchment area. The girls schools are perceived to harder to get into because there are slightly less places -West Kirby/Wirral girls 338 against Calday/Wirral boys 355. However there are more boys than girls in the Wirral population so this evens out.
See the table for 2010 at http://www.wirral.gov.uk/my-services/childrens-services/education-and-learning/schools-and-colleges/school-statistics/number-pupils
What is for sure is that more girls live in the Wirral South Area(catchment Wirral G) than in the Wirral West so Wirral G for girls has always been harder to get into if you are ouitisde the ctachment
e.g 2010 table
Age 7 in Jan 2010 Wirral South 346 in primary schools girls, Wirral West 229 in primary schools
Age 8 in Jan 2010 Wirral South 320 in primary schools, Wirral West 249 in primary schools
This would suggest that statistically for you it's better to go fo West Kirby. This was certainly true in my eldest son's year when one of his class mates was denied a place to Wirral GG although she's passed because she lived in Little Sutton but West Kirby were still taking girls who had changed thier mind about which school to go to. Tghis of course doesn't mean this will happen for the next inatke-as I've already said the population is continuing to fall and the amount of girls in primary schools has fallen by at least 200 since my eldest son took the test in 2007 but you need to make sure you give your DD the best chance of a place by choosing wisely on the preference form
Another plus side is of the Catholic grammars, Upton takes more girls than St Anslems takes boys although it my understanding they offer places to most children who pass and have it as a first preference due to falling population and rschool rolls.
You still have time to prepare but you need to start now . The Wirral exams for Wirral Girls and West Kirby girls consists of 2 verbal reasoning papers compiled by GL assessment. There are 21 types of questions and only 21 types of questions, and your DD will need to know the best way to answer these types of questions.Frankly, some questions are harder than others and the the key things your DD will need to have along with the knowledge of the method and technique is good maths skills and a good vocabularly because some of the words they are expected to know are rarely used in converstion between young people! The good news is that girls are better than boys at the wordy question types.
choice is to use the IPS materials to start with
Buy the IPS method and technique book which shows you how to do each question type, the starter papers pack and the practice papers with the A on the front. Go though the starter papers together and go through each question type in the technique book and show her how to do it using the explanatons in the technique book. After a week or so her loose on her own on the other parctice papers. If you need more then the Tutors materials are also very good and designed with the wirral test in mind. In the summer you'll need to do harder papers so the GL Assement and Bright Saprks ones are more like the real tests. Timing is also crucial but it's more important to embed the method first. Make sure you are using the multiple chocie answer sheets with the materails as the answers on some questuion types can be used can help your DD to answer the questio-you'll spot which ones as you are going through the types. If you get stuck the answer to the problem will normally be somewhere on the forum. Keep reading this and the 11+forum anyway as you'll pick up great tips.
The tests for Upton is completely different and are a combination of verbal reasoning, maths and english so in that sense is more general
Hope this helps