You could certainly start doing some verbal and non-verbal reasoning with her - just pick up some books in Smith's or online. My younger kids all did them from that age because they saw my eldest doing them and wanted to have a go as they looked fun! Whatever happens in the future, she will learn useful skills, vocab, etc from doing them, and you can certainly keep it very low key for the next year.
As for setting her up for disappointment - I think it depends how you pitch it to her. Kendrick is a great school, but it's not going to suit everyone. My dd2 was adamant she wasn't going there, because she likes being at or near the top of the class, and wanted to be appreciated for her hard work, not just seen as normal, lol. She's at a Wokingham borough comp and we're very happy with it - her most recent parents evening was probably the nicest we've ever been to because her teachers were very enthusiastic about her attitude and achievements, rather than the "yup, doing fine" slightly blasé feel we generally come away with from dd1's Kendrick parents' evenings
Which is not to knock it, I think it's a lovely school and it suits dd1 down to the ground.
But you can present it to your daughter as keeping all her options open - go to open days at all the schools you're interested in, and do your best at the Kendrick test so you have the choice of where you'd like to go. As the test and results have been moved before the secondary application date, you don't even have to worry about possibly wasting a CAF choice, so imo there's not really anything to be lost by preparing for it.