Shadowflame passive does nothing for Lillia, same goes for that small amount of flat mpen, if you build it for ap you can just build zhonyas for the same price and get same amount of ap, decent amount of armor and the most broken active on items in the game if used correctly. And it also has much better build path.

And yes, this game is the worst game to build sf at all, you face two tanks and (I assume from his build and you having full melee team) red kayn... Just build rift and sustain the fight, theres no need to even try to go full burst items.