Tonight, I decided I’d have a go at Max Maven’s Mockingbird, which relies upon the Gilbreath principle. I didn’t even get a foot in the door! Having riffle shuffled the cards, I gave her the quarter packs to further mix. That’s when she made a comment about the cards which stopped the trick dead in its tracks.
It sounds like you did the riffle shuffle! I though the point of mocking bird is that the SPECTATOR is doing the riffle shuffle.
Anyway, you clearly have a clever daughter who is fast at "problem solving". Maybe, she noticed that you handled the cards a bit tense, (being clever she got the impression that the cards somehow were prearranged) then when if your kind of count the cards before you give her a pile to shuffle there is not much magic left.
My daughter is a bit the same and is in fact an excellent critic.
Believe me if mocking bird is done flawless the brightest genius in the world have no chance working out this effect.
I have performed this effect as part of my mentalist repertoire, though I now find the effect is a bit too slow to my taste.
Anyway, we all need to test our magic against the most astute spectators, so consider yourself privileged.