The damage isnt huge, but its a fairly inexpensive poke from her Q. It isnt blocked by minions, and is very reliable. The speed of the skillshot means a properly lined up one basicly cant miss, and if you Pix reposition it, then avoiding it is nearly impossible.
Pix reposition means that you place Pix on a minion with your E, then fire glitter lance (Q), and one will come form you, and the other from Pix, much like Zed and his shadow both fire a skillshot. Using Pix both increases your range by putting it on a caster minion, and can radically change the angle you can fire it from.
Lulu also has a decent aa poke game with her passive and the added damage from Pix per aa.
Lastly if you have mana to burn, you can go up to your opponent and hit them with a W, E, aa, Q combo, then walk away. This lets you unload the damaging parts of your kit while theyre polymorphed, and then move away while theyre regaining control. Cost a lot of mana, but they cant offer much reprisal.
For Athenes playstyle you can go up to an enemy, and aa, W, aa, Q (as polymorph is wearing off), then E your ADC to hand over the pix passive + shield (+any healing from blood charges gained from that combo), then move in and Ult yourself to knock up them opponet to chain ALLLL the CC, Q again, Exhaust, aa, aa, aa, and thats how Lulu is the purple menace.
Lulu is strongest against melee assassins, and best supports aa based carries who need peel via her W, and R, because they lack of disengage of their own. Flipside is she also supports melee assassins/fighters on her team with her R, and Q.
If you try her out some more, and are ever in the support position, and you see a couple of
in a comp. Consider getting her. She can shut down most of them with W.
Her damage took a nerf at one point... a big one, but it was because she was so good at everything that they had to take something from her. Shes still viable, and her damage isnt that bad, but it isnt huge (but can be consistent).
Ill say this though, I get most of my use on the Athenes on Karma and Bard. Full charges on Athenes heals for more than the base (uncharged) W at level 5. Its really good for amping the spot heals for mid fight sustain. Karma gets easy charges from RQ hits.