I've picked up Ahri this week, and oh my gosh I have discovered the nightmare that is leblanc. I miss all my skillshots, and farming is stressful. She outfarms me like crazy for some reason. I typically rush Mor 
, because I get a bit of everything for a reasonable price. This puts me in a bad position when LB does get her DFG, but not as bad a position as her having DFG and me still building it (I think).
Help?
Wait until she uses Distortion at you, the Charm because in order to deal damage to you LeBlanc has to get in your face. She has no more silence so, while she is still strong, many champions such as Ahri can take deal with her much more easily.
She's considered one of the best ahri counters. Rush abyssal into dfg and you'll be okay. Focus on farming and playing extremely safe or try to shove her to turret repeatedly like the fizz matchup.
Edit: also try to be rushing dfg over nomicon. Ahri has been forced into the assassin role and mage ahri is kinda dead.
You should always be able to shove leblanc in, that is unless she wastes her spells trying to clear while you only need q.
Try to charm her as she's coming at you with distortion, since it's not a blink you can stop it mid spell and negate the dmg her W is very predictable so with a bit of timing you should be able to stop it quite easily. Once charmed just let go of that combo and back off. Be careful not to get caught by lebancs chain, most smart leblanc will start using w as a reposition to fake out your charm and hit you with EQR or QRE or QER etc.. so be wary and good luck!
Well, I'm not pro but as an Ahri main, LeBlanc is hell to lane against.
Usually I play as passively as possible, farming and staying out of her Q/W range so she can't attack me. I throw out a Q every once in a while so I can at least try to get some poke on her.
Never E-Q-W her or try to combo her when she has mana and when she is in range because I promise you that it's not worth it. You're letting her get close to you and plus, she has all her skills/mana.
What I do is before lv 6, I stay out of range and farm with my AA and Q if needed.
After 6, hell starts. Stay back and Try to poke with Q from far away as possible and just try to dodge all of her skillshots and stay out of the range on her Q. If LeBlanc lands a Q or E, (Her sigil or her chain), be prepared for the worst. Usually after one of those hits, Leblanc will Distort(dash, her W) to you and go right for the kill. Most of the time, she gets it. Her Burst damage is godly and will only get worse.
Mid game is when LeBlanc hits her absolute peak. If she's MIA, ping immediately because LB might be roaming. A Roaming LB will usually cause your team to rage and in some cases, surrender. LB will fall of Late-Game, but only if your team lasts that long.
Once LB has no mana left, or has just used her W, which has quite a long CD during early levels, you can do some more poking. Once she's at around 60% health with no mana, it's okay to try for the kill. Initiate with your E, or if you're so positive it will land, your R then E, and go for Q, 
,W. The reason why you is because of LB's passive. Ignite will allow you to see which one is the real LB and which on is a clone. Chasing LB down with R works the best for me.
A good LB is never afraid to tower dive. Land a E, Q, W, R and you're dead. Even under the tower.
I usually build 
and in some extreme cases
+
if I must. With some practice and some experimentation, LB is still hard to lane against for me, but it has gotten much better. You can't win mid-game against her, you can only outplay and outscale late game.
DFG is pretty useful. I like it, but there are better things to build against a LB. It's a deadly tool for the Assassin Ahri play style. I usually get this after or
Any last words? The best way to counter a champion is to fully understand and know how to play them. Once LB comes on free, try playing her. Once you understand how she works I 
-tee that life will be so much better.
At least you weren't playing ahri when lb had silence.... those were some dark times...
In my experience the key to beating LB is never fighting her. You fight her and she will easily outburst you. Build Chalice for Mana Regen and MR and constantly shove her under turret. Farming for an LB is a nightmare under turret and she ends up blowing her mana and her distortion just trying to get CS. For ahri it gets safer post-6 because she has that mobility incase for ganks and for the outplay potential incase LB commits to fighting you
when fighting LB, stay near minions so she cant chain you. the moment she dives you. ult into the minions to avoid her chain and while staying close to her so she eats all the damage. you can try to charm her but I recommend charming her at close range so she has a harder time dodging it. As long as you can do more damage and handle her burst, you got the upper hand. I recommend getting a lot of mr and hp items like athene's grail, abyssal sceptor, rylai, and rod. you can pick up a deathcap but I would get a void staff if they got tanks on the team instead.
