As a Lux main I understand how sometimes easy it is to dominate lane and carry your ADC. However, if you are able to dodge, Lux's Q and E she is pretty much useless. She only gets that extra damage on you if an ability hits you. You can see her Q coming, it is not lock on - easy to dodge, you can also see her E which is reasonably easy to dodge too.
You want to try to stop her from getting gold early game, so if she has bought Spell Thief try to not be in auto attack range or get hit by her abilities as this gives her 10/20 gold every time she hits you. Stopping her from doing this would put her behind on items and therefor do less damage.
I find Pyke, Thresh and Blitz are the worst to lane against so if you want to counter her play someone with a hook and hopefully your ADC will be able to kill her - she is very squishy.
If you are playing as a tank she doesn't really do to much damage even with the items that she would build to kill you. She is only a threat if she has someone who actually does damage to you such as Kaisa, Vayne etc with her.
You can also build items that cancel cc against her, such as QSS or Mikael's Crucible which would stop her from getting her combos off.
(Remember her Q is only a root you can still cast and auto attack whilst rooted).
I hope this helps!
[sg-ahri-2]