there could be another way to give her a stealth-concept that actually doesnt neccessarily have to make her PERMANENTLY INVISIBLE.
it simply is nothing that makes the game better or more interesting. also, having such a strong passive, probably the strongest passive in the game, means alot of her power has to be taken away from other abilities and its logically impossible to balance this correctly because she MUST BE a much weaker fighter than any other champion.
she must be very squishy and her damage has to be limited in range (which it is) but if shes too squishy, she is useless and if she isnt squishy enough, her invisibility is too strong. its simply the yasuo syndrome where the kit of a champion is in a spot where it cant be balanced.
yasuos entire kit either contains enough damage to enables him to do his job in which case he is overpowered or it doesnt, in which case he is underpowered. either he can kill, in which case he has EVERYTHING or he cant kill, in which case he only has mediocre mobility and mediocre utility. there is no middle ground because he is a killer. if he cant kill, you wouldnt want to pick yasuo.
same with evelyn. she must pay for her invisibility so if her damage is so high that she can kill you if she gets close, invisibility is too strong because it enables her to get close very easily. if her damage is too low to kill you, its still very strong because she can choose when to deal it.
if her damage is low enough for her passive to not be overpowered, its too low for her passive to be impactful. also, her concept is based on being super squishy but darting in and out of shadows to not be targeted. this means if she is too squishy, the invisibility doesnt help and if she isnt too squishy, its overpowered.
there is no middle ground. its a bad concept and it should be removed.