The Counter to Illaoi
Just dodge shit.
Q: sidestep. Like seriously. Just move to the side about the width of one Teemo, and you're safe.
W: sure, she'll get the initial damage off if you go in range. (If possible, don't). If you get hit by W, just follow the instructions for Q. Dodge those tentacles, bb
E: ever played against Blitz, Thresh, Naut? Then you know what to do for this. Stay behind minions If she does get your spirit, smack the shit out of her. If she keeps hitting your spirit, voila. You won a trade. If she doesn't, keep fighting until your spirit goes away. If for some reason she kills the spirit or you have to run away, kill dem tentacles. When they spawn, dodge then kill. Any tentacles in the lane count toward the 3 you need.
R: if she hits you with her ult, just disengage. Wait until the tentacles won't smack you every 2 seconds.
How to avoid some of her abilities:
Walk toward a tentacle on a wall. Back up. Good job, you just baited out her Q or E.
Proceed to win lane.