Magic resist.

So your pushed out of lane by 2 abilities and you have maybe 250-400 gold. Build null magic mantle? She still insta****s you if you get close to farm. If you stack MR your going to be useless and do 0 damage and still lose to her 1v1 because she blinks away and kites

Go for items like Abyssals early, maybe mg resist boots, then sell them for magic pen after laning phase

Here's how you counter LeBlanc:

Use your first 740 gold (if you can't get 40 CS before she hits level 6, you deserve to lose to her) to buy a negatron cloak. Buy 2 doran's. Continue with your usual build, laughing as your enemy has nothing from a useless AP carry.

abysal isnt enough to let you get near her and by the time you manage to afford it she has 20 stacks mejais deathcap and void staff. Really all i can see working is playing galio

play karth and farm from ur tower. if she comes in to range

exaust, defile, wall to slow her more and Q her to death.

also when u farm under tower she has to extend out and can be easily ganked by jungler

Although it would lower your damage, a Banshees is the #1 counter to her.

so your going to go banshees first as the ap?....