Do not play against her. If you do end up against her, try your best to stay under your tower. If you leave it's vicinity, even for CS, she will dash behind you and kill you. If she doesn't finish you, she will cripple your farming for the entire game, by putting you at such a low level, and she will snowball very hard.If somehow you manage to kill here, take advantage of it to farm as much as you can. Try to get your Runaan's Hurricane before she get her first major item to increase CS.