As someone who plays her with relative frequency I agree that she's a bit too hard to do anything against after level 2.
She can jump in and out for free harass, and as long as she's not over-harassing, and continues to last hit minions, she can sustain fairly well in terms of mana, on a single or double doran's ring purchase, depending on how fast you can get to your morellos.
The issue with LeBlanc, comes with when her jungler is actually helpful, she gets blue, can harass all day long with no worries, and then roams that blue buff all over the map to punish the other lanes.
Being that she's extremely safe all the time, she's just a solid pick up. I think my worst game since I started really playing her this year was a loss where I finished 10/7/9, and that was due to a jungler that DCed about 6 times during the game. I've had 3 games where I didn't die at all, one of which I finished with a 28 KDA. I think her mobility is the issue, but without reworking the champion entirely I can't think of a way to mitigate that.