As mentioned in the notes, BorK aids her weak early game while offering life steal and attack speed. Black cleaver's 20% CDR is key, much like lucain, in that this build focuses around utilizing you abilities not your auto attacks and frozen mallet aids this due to its passive allow you to land your e (stun) much more easily, slowing the enemy down allows you to proc your passive w/ q/w and land feathers infront/behind the enemy and activating your stun. This core focuses around surviving skirmishes and team fights after all if you're alive you can deal damage. lastly the 2 free slots for situational items mean you can build more damage through crit/as items or more defensively to aid survivability.

I realise this is not optimal but using this build myself for over 10 games have 90% win rate with extreamly high KDA's and surprisingly high damage output, often doing the most damage.