My DS4 took the SB-V when he was 4.1. Since my son doesn't like doing things he's already done, I told him he should answer all the questions even if they seem silly or too easy, because you have to answer all the questions to get to the more fun and interesting questions.
My son was like your daughter - he had bad experiences with the doctor right before the test, so I had to reassure him there would be no needles whatsoever, and this was only a thinking test.
Since he was new to being alone with a stranger, we talked for a week or two ahead of time that he would be in a different room with the test administrator. I also showed him her picture.
Taking advice from others here, I also told him he could ask for breaks whenever he wanted. It turned out he loved the test and only took a very short version of the planned break.
I told him that the test was to find out how he thinks compared to other kids his age, and that it would help us to decide what kind of school he would go to.
Good luck!
