Leblanc is really, really, really bad.

Kat, especially, is really good against her.

pre 6, every time she hits you with her q, shunpo to a minion(sometimes even to her) to avoid getting hit by her dash. This gets rid of almost all of her dmg, and the silence as well. Use the rest of your spells on her, and you will win every trade.

Other pre 6 lane tactics are to shove the lane, so that she's forced to either lose cs, or use spells to farm minions under her tower. Leblanc is terrible at farming under tower, and she has mana problems too, so either she gets to have no money, or no mana to fight you with. Ward the enemy wraiths, push the lane, and lie in wait for the enemy jungler so you can assassinate him when he's low. Check red too, junglers often do red at under half health. Sometimes, just steal the wraiths and leave. Don't stay there long enough to lose cs though.

Alternatively, shove the lane, and then gank top or bot for some easy kills, b then come back to lane stronger/with more items than her.

After you've gimped their jungler, and their mid has little to no cs, you can buy either a negatron cloak, or for a little bit more, a giants belt. I prefer giants belt, because a quick rylai's decimates her dmg, gives you sticking power, and helps your ganks a ton. Follow that up with either abyssal's, or qss(get rid of the silence, and then immediately shunpo ult to her, rips her to pieces).

Leblanc is a really bad champion, she's in a pretty bad position right now. Kat is probably one of the most OP mages in the game. Getting to face LB as Kat is a joke.

Balanced? Whats Balanced? Never heard of such thing

Xerath. Owns. Her. Poke her with W-Q. Keep poking her. Dont stop, and dont you dare miss. Just poke poke poke poke. Dont go for the kill. Dont get too close. Short sentences. Eventually 1 of 2 things will happen. She will recall, giving you time to go buy, or keep farming, or she will say **** it and attack you with blink/sigil combo, at which point you pop E on her, she blinks away, W and Q her. If done correctly she will either be almost dead or a lot closer to it. Know that distance that someone can flash up to you and nuke you? Stay outside that range of leblanc starting at level 2. Past 6 you can follow up with R-R-R-and another Q to really instill fear in this bish. I love going agianst leblanc on xerath. gives me much joy :3

Just buy magick resist and some potions, she's very mana starving...

Play draft pick. Problem solved. She is easily countered by a good amount of champs. Veiger post 6 will destroy a careless LB. Sivir, Nocturne, Ahri, Fiddle, Galio, Karthus(not a counter but an easy passive lane),Gragas, Malzahar, Morgana, Orianna, Xerath.

Anybody that can push a lane hard with range is good. She cant farm under her tower easily. Anybody with good harass dmg will make her more passive in lane and hig HP/MR champs are good.

I read the first page and I have to say this to the OP.

I'm going to assume that despite the fact that you can't figure out this problem, you have access to understand relatively basic logic. Leblanc is not currently crowning the meta (in fact, I think Leblanc is a rather easy opponent to deal with). Leblanc is very rarely chosen in higher level play. Basic logic can then lead you to conclude that Leblanc has a weakness, and is quite conquerable.

Branching from that, it is safe to conclude that people who have come in here, given you advice, and received many upvotes are probably correct. I myself, immediately rush Negatron Cloak when I see Leblanc (and dodge her skill shot) and find that I'm able to survive quite easily. I also make sure I am also harassing Leblanc instead of just being afraid of her harassment to me, especially before level 6. Often, Leblanc must blink into range to land her attacks, which means that she's using a lot of mana to try and poke successfully. Being that Katarina is a mobile/manaless champion, you can push the wave against Leblanc for free, and simply stay out of range of her damage (Sigil of Silence has 700 range, btw). This means that through effective defensive playing (which doesn't mean not poking ever), you can starve Leblanc of Mana, and then you will become a lane bully.

Instead of coming in here with a "remove this low tier champion from the game mentality because I am bad" you should actually LISTEN to the advice other people give you, and if you are unsure of how this advice works, you should ASK for additional clarification, instead of just rejecting the core strategies which are tried and true proven successful. You are currently using a scrub mentality of "I don't know what to do right away so therefore it must be broken" and ignoring those trying to help you.

As an additional note, I would NOT buy a Doran's Ring on Kat because she cannot really benefit from Mana Regeneration. Instead, I would simply buy Health Potions to heal off the poke that she is landing on you. If you are farming correctly and poking back, Health Potions are an excellent way to circumvent poke and help you sustain in lane, especially since you will be building a Negatron Cloak before your Hextech Revolver.

As a final tip, I think in some match-ups, you will be very surprised to find how effect an early Kindlegem can be on Katarina (this can be sold late game when rounding out your build). Outside of Rylai's Crystal Scepter, Katarina finds it difficult to build Health items that do not give her stats she does not want. However, Kindlegem provides CDR, which actually multiplies her damage, as she does not need to be concerned about mana, enabling you to act more frequently, in addition to increasing your survivablity. Considering that CDR is both rare and powerful on Katarina, I think that this will be a great item for you if you find yourself dying too easily in lane. I would not build until after your Hextech Revolver though. Alternatively, you can build a Heart of Gold and then sell it later just like every other champion in the game that needs cheap health (until it gets removed, of course, for this exact reason).
But outside of using customized building outside of items in your core build path, I think Health Potions will do just fine, after you have yourself a Negatron Cloak.

dooop

Don't let her hit you. She is weak unless you're bold enough to let her full combo you... xP