Mejai's can be a good item on her since she's pretty safe, but when do you get it? Should you get it early game even if you're like 0/0/0, or wait till midgame when the dragon fights break out (assuming you're not really behind)?
I don't think you should get it unless either you or your frontline is incredibly fed and you have enough mana regen to be able to get loads of assists/kills without much effort. The cost effectiveness fluctuates with the amount of stacks, so if you're outplayed you have to get more stacks to justify still having it.
Personally, I wouldn't recommend getting it unless you're duo-queueing and you and at least one other teammate (preferably one of your tanks or bruisers) are doing really well. I haven't bought it on Lux for ages, mostly because I don't usually duo and I don't like putting that big of a target on myself.
