Depends on your champion.
If you have great pushing power and relative safety like Zed, push her into her tower and she will lose tons of CS.
Lux is terrible at last hitting with her long CD, bad shoving power and the time she needs to take to wipe mobs with auto attacks give you free reign over the lane and if she try to attack you, she will simply lose more CS.
It also give you the chance to roam and help other lanes.
If you have killing power like Fizz, try letting her push a little and ask for a jungler gank to shut her down early. If the jungler can't or won't come, wait for the minions to not be stacked in her favor before making your move. Make sure you dodge that Q or you'll screw yourself over. Once her Q and E are gone, she's vulnerable and will usually retreat, keep attacking and count the seconds to make sure you can retreat before her Q is back or better yet, kill her outright.
If you are a farmer, just stay safe of her Q and passive when she E you and outsustain her poke. She won't do shit for poke if she doesn't land an auto attack after her E. Punish her when she goes past your minion line has your minions will help you trade against her.
Honestly, the best way to beat her is to deny her CS and punish her when she try to last hit. A good Lux is hard to kill, but even a good Lux needs to auto if they want all their CS.