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.

BorK provides a stronger presence in the early game with additional life steal, ad and life steal, also a useful item when dealing with tanks or trades/skirmishes.

Black cleaver offers 20% CDR that is extremely handy as this guide focuses on your abilities more so then auto attacks, again this item means you can totally shred any tank thats tried to dive or cc you as well as having additional health to keep you alive

Lastly frozen mallet aids your kiting potential even further due to its passive, can be used to disengage oncoming enemies like tanks or hunt down squishies and land your stun more easily. Again the additional health makes sure it takes more then a zed ult to kill you.

These are the standard situational items that are dependent on the enemy and your teams compositions. Heavy cc should be answered with a QSS into mercurial scim, high ability power should be answered by a Maw (also offers additional CDR and a very helpful passive for even more survivability.) Last whisper is nearly always key for any adc but depending on who you are attacking determines which item would be better suited, i.e. LDR is much more effective nine times out of ten in battling tanks where as Mortal Reminder is only really useful against champions like Vlad, Swain and Mundo.

If you need more damage an Infinity Edge + a zeal item (PD or RFC) is a good way to round out the build, or you can replace the IE with an essence reaver for the maxed out CDR. Even more so a Blood Thirster is a classic choice offering high damage, high sustain and a beneficial passive in the shield.