I guess this is one good side for never having tested DS, I can't tell him what I don't know.
As a parent of a teens I tend to dislike the idea of telling a child that they can't know something until they turn 18. Because it's likely they are going to find out on their own, and then won't talk to you about it because it's forbidden. IMO by the time a kid is in High School they should be involved in advocating for themselves and be privy to this kind of information if they want it. That doesn't mean a 9 year old needs to know her IQ.
I am curious what are you worried will happen if she knows her IQ? Perhaps if you think about this carefully it will help you figure out how best to respond. Sounds like you need to have a discussion about why she wants this information and what she is going to do with it. I agree with the other posters that perhaps you can explain what range her IQ is in, rather than the actual number.
