I sometimes skill Q, the slow is useful for invades or for early fights but in lane mitigating the harass on your ADC is paramount so her shield is very nice. I don't do the thing some folks do, which is level Q a lot and try to poke endlessly. I go more for utility, leveling her E a few levels and skilling a lot in her W for increased squrrel duration. Who wouldn't want to turn darius into a squrrel for longer?
I consider crucible to be very core on lulu, as well as surelias and frost queens claim, either of them. I prefer the AP one because my main focus is getting high AP to make my shield strong and my passive hit hard when i shield some one (my passive gives my ADC for example like 26 magic damage on hit + the base value which i think is 14.45 or something. It adds a lot of damage and with it just makes your vayne or whoever you happen to be supporting very happy to clean up while you peel like a boss and use your ultimate, crucible and frost queen slow+ your other abilties to turn teamfights in your teams favor consistently.