Anyone who needs starting items is going to have problems. You do a lot of damage and with your shield, you are dangerous with out any items starting at level 1 and it doesn't stop. Clear the camps until you hit level 3, then you can start to gank if a lane needs help. If they ever push towards your towers, gank them and make them think twice about it. At 6, you separate their team and trap them in a box for yours. Every gank bot lane should be a kill.

The reason the core items are blood razor and triforce deal with the note on the section. At level 16, her Q does 100% true damage on the 2nd hit. This matters because it does it for the bonus triforce damage and the blood razor damage. Even before 16, this is a lot of extra damage being added on. Every 3 seconds, with CDR, means you are dealing 4% of their max health as bonus true damage. Needless to say, everything adds up. The constantly auto attacks and triforce mixed with your hefty shield leave for not much left to do against her.