Leblanc is not hard to play against. Annie is good against her, so is Diana. Heimer's turrets hurt her a lot, plus they push the wave so she can't really hurt you. If you can play Zed well, he can counter her as well. Even Lux can be good if you can land your skillshots since you can stand back. They rarely ever build MR and if you do, then she won't hurt as bad. Plus, doing her Q + W + E takes a lot of mana. When she uses her W for any reason, use this time to punish her. I played Brand for the first time in a long time on 5v5s (played him a few times on ARAM) and I went against a Leblanc. She would try to all in me and I could E + Q her to stun her then W where she was stunned. Anything with CC or high burst can counter her.
If you get right in her face then you may be punished, but after she uses her W then punish her back, or try to have your jungler gank at that time because she has no esacpes pre 6. And when she is 6, her ult has about a 30 sec cool down so you have a little bit of time to punish her. I suggest you try her and figure out her weaknesses so that way you can play against her.