LeBlanc is a great champion, especially early-mid game, so it's obvious that she will rock in a faster 3vs3 system. Although she is really good 5vs5 too but her true potential is the early game annihilation so a smaller map is preferable. You can gank extreamly well cuz of your insane burst dmg with more then sufficent escaping skills. On Twisted Treeline you have generally less time to farm and gain money before ganks, so you need champs that can fare well without the badass items. I want to say i understand that Twisted Treeline is mainly for low-level players, however i think it can be really funny, also its better to gain some IP if needed.
So let's get started!

Pros:
-very high dmg
-not depending on items
-good escape skills
-silence, slow
-you will be the hottest in the match

Cons:
-pretty squishy
-after combo you are completly useless
-need top badly
-having some trouble against tanks
-late game not that effective

Mastery tree is the standard spellcaster layout 9/0/21. Altough some damage increase can be gained if you go offence tree, but imo it does not worth it. With utility you will gain some mana reg with a nice cooldown reduction. To tell you the turth i havent tried out the defense tree yet, but i belive its not work on this map cuz of the lack of time and items, but as always feel free to experiment.

Runes are simple Greater Mark of Magic Penetration for magic penetration, seals for mana reg/5 Greater Seal of Replenishment glyphs for ability power Glyph of Ability Power and quintessence too Greater Quintessence of Ability Power. You can use level dependent runes too, though they dont do much difference, but since these matches rarely last till lvl 18 i dont see them usefull here. Another option is the full AP page which can definitely punish your enemies early game but you will run out of mana pretty fast and later you will miss the armor penetration too, but clearly a viable option.

Summoner spells are very important and can win matches for you. One is a must while the other is up for you, but i will give some alternatives. Ignite is your best friend. It will help you get FB, you can annoy champs who like to regenerate and also can do pretty nice dmg. Moreover if you go Offence skill tree it gives 10 more AP if its on CD. Awesome. The other one can be Ghost, which is good for escaping, i wouldnt say its needed for chasing since you cant really chase them cuz probably your skills are on CD. If you dont istagib them move on. Other options are Heal which can be pretty useful in the early ganks. Also Exhaust can be used for almost sure FB with Ignite and also for escaping. (chasing isnt a true option again)

Since mostly your skills will do the damage items are not that important, but dont get me wrong if you dont get your necessary stuff, you wont do well.
I always start with a Doran's Ring it gives you hp, ability power with mana reg. Perfect. After that stay out until around lvl 7, at that you should have about 1-1.2k money so go back and grab Sorcerer's Shoes. This is when gank starts, you got all your items you need and most importantly you got Mimic. After that get Mejai's Soulstealer. Even though most likely you wont get max stacks, with about 5 kill you can get 100 AP for 1200 money which totally worth it. If you dont feel comfortable you can get a Needlessly Large Rod for a little bit more money but a permanent AP with a path to build it into a Rabadon's Deathcap. At that point your are around lvl 11 so you probably face some dmg items from the other team so you need some protection. Banshee's Veil is the best choice imo. It gives magic resistance, hp, mp, and a free Cleanse spell. At that point the game is usually over. If not go and get Rabadon's Deathcap. If its still not enough surrender, you do something wrong. Wahaha:D

The most important part of LeBlanc is the skilling. You have to practice it cuz you will need to cast combos very fast since you have to take them down before they take you down. On early levels just focus on last hitting, with some Sigil of Silence to your opponent so he wont be too jumpy. After you hit level 6-7 the fun part begins. 1 thing is very important. You always want to gank them from behind, you cant go front attack you need to suprise your enemy. Just cast Sigil of Silence then Mimic followed by a Distortion after that immediately by an Ethereal Chains. While chained use an Ignite and some autoattack. After chain trigger your Sigil of Silence should be off the CD, use it if needed. Needless to say in most cases you dont need all these skills, but this is the base if less needed its only good for you. With this you should be able to bring down everything except tanks. So just roam around the map (carefully hide your movement), buy some wards and take down lonely champions. After some kills the enemy team will fear to go alone so thats when you should group up too. Get the dragon and finish them off. Wait for your tank or high hp guy to initiate then target the enemy squishy champ take him down do as much dmg as you can to the other champs then retreat. Simly as that.

First thank you for reading this guide. If you willing to spend some time and practice LeBlanc you will find out that she is more powerful than you first thought. Also i know that Summoner's Rift is the main map i dont doubt it, but playing some on Twisted Treeline is fun and Leblanc is extremely good on it.