MR does help, but you have to remember, she was designed to be very good in lane; as the game progresses she will get weaker and weaker.

dodge, lol.

Something is wrong woth you if you feed her that hard. Play someone who can be built around defensive building and still do good dps like ryze or banshees will ruin her combo and ryze can push the lane much faster ( not the best before 6 push ).

Galio's damage scales on MR which means you can just completely **** her up while still staying on a high burst high ap build.

Vladamir can build hp which givea him ap in return and vice versa. Its not the best for fighting her but it can still work out and his lane pushing is great.

Fizz has good durability and jukes and can make himself untargetable. His lane push sux but his ability to kill leblanc is good because most of his dps is delayed and DoT.

Thought I should throw in my two cents, since I used to play Leblanc quite a bit, and still do on occasion.

First off, you should have MR per level Glyphs. The blue ones, if I'm correct, for pretty much mid altogether. Also, health per level seals, the yellow ones, are good for mitigating burst damage.

During the early levels, she is going to Q harass and try to proc the debuff whenever possible. One choice is to try and exchange, pretty much don't be a *****. You'll be surprised how much damage you can actually pull off exchanging pre lvl 6, as leblanc's total burst revolves around her ult. Your other choice is to push the **** out of lane. Leblanc cannot farm effectively AND harass you at the same time. She either wastes mana securing cs, or throwing her spells at you. She can't do both. In my opinion, just play someone that can push the lane hard, push it out to her tower, then go farm wraiths or gank a lane. Leblanc will either have to sacrifice the wave you pushed to tower to follow you, or stay and farm at tower. Kat is decent in her Q-W combo in pushing the wave.

Now, that early burst damage by Leblanc is quite the *****. The best way to mitigate her early burst damage like that is actually health, and not MR. MR is good, yes, but buying an early giant's belt is better against Leblanc, since, as Kat, you are going to build a rylai's later, anyways. Also, going merc treads instead of your usual sorc boots will not only reduce Leblanc's overall damage, but shorten both the silence and chain snare.

Some other things to keep in mind, Leblanc is really strong during laning phase, as she can not only out-damage just about anyone she faces in lane, but also walk up and down lanes and put out gap-closing, large bursted ganks. However, Leblanc falls really hard once teams start grouping, as she wants to surprise targets that are singled out. Kind of hard to do that when the enemy team is grouped.
Another note, Kat isn't all that dominant in lane, which only widens the gap between these two. Katarina shines at ganking other lanes and teamfights, where her team can protect her from cc. Just remember to build a little tankier than usual, and you should be fine. Abyssal's, Rylai's, merc treads should be decent enough. A well timed Zhonya's should do the trick after that.

BTW if anybody has 20 stacks of ANYTHING, that is entirely your fault at making bad choices. The match-up doesn't matter. That is just being downright outplayed if anyone gets full stacks.

Banshees first as AP isn't that bad. The bad thing is having you rage about LB. You should probably be using MR or HP per level runes somewhere in your set. I have no clue what your skill level is. Are you a lvl30 yet?

Wouldnt work I main lb... I would prob just dive you pull of my whole combo except my ult and get away with a tower shot. Wait for CD then come back with my combo and ult and kill you only taking a total of 2 tower shots. Early tip harass her hard lvl 1 she got nothing if they don't have a mana pendant they will run outta man so fast. She only has burst so if you are harassing her and she takes 1/4 of your health don't run, she now has to wait on CD. You can dodge her E if you try (its seriously so easy to dodge I use it to escape instead of initiating). Just some tips.

Here's where I get irritated. You ask for advice and then shoot down the sensible advice you're given. Since you clearly don't know what the actual **** is going on here, you should just listen to the damned advice and shut up.

LeBlanc won't have 20 stacked Mejai's, Deathcap, and Void Staff by lv.6. That's not possible. Even if she killed you ten times in as many minutes and picked up every last hit in the lane and farmed every wraith camp, which is impossible due to her mana constraints, she wouldn't have enough gold to buy all of that.

Abyssal Scepter beats the hell out of LeBlanc. Also, late game, she won't have the range in teamfights to do anything but blow up the nearest person, which should be the TDPS charging at her. Wait for her sigils to fly out and then jump in if you're Kat.

Plus if you buy Banshee's LeBlanc is literally worthless. You negate her first Sigil, she can't pop her ultimate sigil because she had to use her jump to get in range (And if she was already in range you're an idiot for being careless) and she can't land her snare to proc the sigil against anyone with 370 movement speed.

My two main mid champions laugh in leblanc's face. Mordekaiser and Kassadin both counter leblanc quite well. Mordekaiser has good sustain and can push leblanc out of lane and Kassadin is just an anti-caster in general and counters most casters. Kassadin's early game is rough but once he hits level 6 people run and scurry because of his ulti.

Get a negatron your first trip back. Play a passive farm lane. So long as you don't feed her kills she will be useless once the teamfights start while you will not.

That's your problem you're playing Kat against Leblanc. Why would you EVER do that? Also, if your worried about her pick a champ that can withstand her early game burst like Galio or Fizz? Or just play an ad mid like Pantheon or Talon. This is also a perfect example of when Cho'gath would be good mid as well, considering Cho is too tanky for LB to burst down, Cho can poke her with his q and if she does get dumb enough to come close, silence, rupture, eat her face.