I am sure it has nothing to do with "happiness" but with "luck". meaning the "trébol" symbol on the cellphone must have 4 leafs.
If you chose the "unlucky" title when beginning the game (like i did), then you are a bit screw, since you will need to to fully develop the relationship with lavish, and receive 2 christmas presents from her to get her "lucky panties".
Only then with them and using a 4 leafs trébol before sleeping will you get the second dream with emma.
if you didn't chose the unlucky title, then just use a 4 leafs trevol before sleeping in the night. You should see the second dream and then you can meet her on the park later.