I just played a game where enemy lux had 172 armor

87.6 base armor at lv 18, 45 armor from zhonya's, could've used scaling armor yellows which would be 27 at lv 18, with resolve mastery and some other points in armor scattered in the runes it's pretty easy for Lux to get 172 armor.

With the power of mysteries, anything is possible.

no, her own armor, the mastery that gives 5% to bonus armor and scaling armor runes its easy + who ever was in tha game giving her more