I guess it's making her dance that's the 3rd secret.

UPD. Nope, got all three secrets (though couldn't reproduce the 3rd one), so it turns out the "dance" button is just not working.
UPD2. Okay, reproduced the 3rd one. Gonna investigate on dancing. If it really depends on her mood (as she says), then I guess the mood must be the worst one possible, because the first time I tried she had the best mood possible.
UPD3. Tried with the worst one - still no luck.