leblanc literally just 100-0'd me at lvl 3 with just q w ignite

Well It's normal mate depending of your MR, if she goes full ap or not, If you got Hp on masteries or if you goes for movespeed etc. LB is an assassin.

At least you're not playing Dota where a Nuker can press 1 key and you're dead, no matter your hp and your lvl ^^

what are the base stats of the champ you were playing? had she gone back to buy? what were your runes? what is your favorite color?