Last night I accidently got the cheif to point out a new item to a child. I tried again, and it said "can only do once in twenty four hours".

I've tried several times tonight, but she lectures, tells stories and says "can only do once in twenty four hours".

What is it that I did the first time? What do I need to do for her to know that I want her to point out new items in the collections instead of all the other things she likes to do?

Did you wait the Full 24 Hours?

If you click on the "?" next to Leadership tech on the Tech screen, you will see a description of how to repeat what you did, but all of the chief's special abilities can be performed only once every 24 real hours (according to your computer's system clock).

In addition, remember that these are pixels; they have no knowledge except what the programmers give them, and can do nothing except what they're programmed to do. The chief points out a random rare collectible every time that power is used; that's the way that ability works. You can't ask her very nicely to point out something you don't have yet, because that's not the way she's programmed to perform that ability.