Leblanc Main here.
Have played her and mained her since lvl 12 and I agree with almost everything paragon has said here.
Summoner Spells. Exhaust while being good is often hard to use in time to combat a good leblanc. I feel that barrier is a much better alternative here. Leblancs combos after lvl 3 with happen about every 14 secs once all her cooldowns come off, this makes exhausting kind of pointless since often you will not be able to get it off before she starts it. and if you do manage to time the exhaust a good lb will simply stop attacking and save the rest of her spells for the next all in. SO you either take the instant dmg form qw and waste exhaust or you exhaust and she jsut doesnt all in and backs off waiting for it to simply wear off. This makes Barrier a much better summoner since it will likely counter both her ignite and her burst dmg DURING her all in were its important to survive.
Another note is that often on any w combo you can reliably auto attack leblanc when she goes in especially with these ranged champs. If you dont have a spell to hit her with at least trade an auto attack when she distortions in. Its easy to cancel this auto on her to make sure you let it play out the animation. IF you fail to trade back initially when she dashes in look to her landing pad and immediately as liss aim your q there. Most lbs even good ones have bad habits of jumping back to their return pad thinking they are safe. Its a huge habit and will get you alot of free skill shots on her. Especially if you play ahri and want to hit charm ect.
I dont necessarily agree with pushing on leblanc. In Bronze/silver maybe. But if its a 50+ game leblanc player or a good player often its a bad idea to continuously push on her. Leblanc is basically a mobile version of ryze. the more spells it takes her to get to you the less dmg she has. If your pushing consistently to her tower in lane I would have free easy kill pressure not to mention jg help. bad Leblancs will have trouble last hitting under tower and will lose cs but at the higher lvls the leblanc can easily use a combo on you in the middle of lane. have an easier times of hitting chains and immediately blink back to her OWN tower if you retaliate. This last part her ability to get to safety quickly is the big one.
If anything I would try to either freeze or slow freeze so that leblanc is stuck in the middle of lane. If your near your tower with either champ you can cc her under tower if she dives you. 2nd if she does roam since every other champ can push faster than her she will lose tower fast to you since when she comes back she cant push very well. Also if you ever do get a jg gank your only chance to really trap her is if she is far enough away from her own tower that she cant distortion back far enough immediately to get to her tower.
Also you basically win this lane if she doesnt do well early. Both your champions scale much better or have more utility in team fights than the average leblanc. A good leblanc player will always be scary though like a good riven or lee sin.
Also I have faces several good cassio players and one who beat me in lane took ms quints and harassed and chased me out of lane pretty consistently early. Id give those a try. They help your range and harass alot through how deceiving it is with the speed increase. She took a pair of boots relatively early too like 2nd back