I've been trying LB in the crystal scar and have been doing pretty great, but I'm trying to decide what the best possible starting items would be.

I haven't won a Dominion game with her, as our teams overall weren't doing well, but I got 1st both times and the last time I got a triple kill.

So anyways, I think she actually is good in Dominion, despite most people insisting she isn't.

I've been doing well in dominion playing LB both bot and top. I go boots of speed, prospector's ring, and two health pots to start. Then i build wooglet's, morello's, and Will of the Ancient's. You could probably substitute the last 2 items for a deathfire and finish off with a void staff though depending on what you like. (I don't like having to activate items.)

Glass cannon is the only way to go with Leblanc in Dominion. It's possible to play her otherwise but you will not be as successful. LB is designed to slaughter one person each burst; you get high k/d/a very easily. However she isn't very useful outside of killing people, which isn't the point of Dom, keep that in mind.

Prospecters Ring, Boots, Health Pot start.
Magic Pen boots
Haunting Guise
BFT (or the other Mask if you don't like BFT)
Void
Wooglets
~~insert other AP item here

After that it's fair game. This will give you ridiculous burst, you will smash any champion below the Tanky DPS line no problem, just beware MR. The massive amount of early Magic Pen should keep your damage up though.