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
BFT (or the other Mask if you don't like BFT)
~~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.