Hi Mag,
For a child that takes her time and thinks things through, if possible, months or weeks before the test, role play and play games about making mistakes and how it is ok.
Have child go through multiple scenarios where they have to guess and not know their answer is right/wrong. Like how many jelly beans in a (small) jar etc. Then get to eat it!
Show how you/parents deal with mistakes and the "oh well" and "oops" didn't get it right, smile, shrug, move on, etc. I'm sure you know all this already, just saying.
Having a good tester is very important. Knows just enough to move the child along but will wait for those un-timed questions. And is happy to let the child think and think. Won't rush the child. Will encourage the child to take a wild guess. Say things like "you're not suppose to know these, it is just for fun" etc
hope that helps a bit
