You've itemized for increasing autoattack damage, so it will represent a slightly larger percentage of her damage. However, you haven't itemized to support the major source of your damage, which is abilities, not autoattacks. You are doing more damage with autoattacks, but you are doing less damage than you could be if your abilities were stronger.
Let me explain this. Crit enhances autoattack damage. It purely boosts damage from autoattacking, and nothing else. Armor penetration boosts all physical damage, but doesn't boost autoattacks as much as crit does, making it more suited to abilities. Champions who get higher percentages of their damage from autoattacking (AD carries, Trynd, etc) buy crit because it enhances their primary source of damage. They buy more autoattack scaling (persistent attack speed), which also makes other autoattack scaling mechanics stronger. However, bruisers like Vi do a higher percentage of their damage with abilities. This makes armor penetration, CDR, and flat AD more desirable stats, because they boost her primary damage source while crit doesn't.
I can always do more damage for my money on Vi buying armor penetration and flat AD than buying crit, and I can do it while getting earlier power spikes from brutalizers, getting more CDR (which is good, because every point of CDR makes every other point of CDR stronger). It's better unless you are doing a hell of a lot more damage just from autoattacks than Vi does. This holds true for almost any bruiser. Armor penetration is almost always a better stat for them than crit.
IE is not a good item for her unless you in a 55+ minute game and you're trying to get as slot-efficient a build as you can. It's less damage for the money than you can get with other options. It should absolutely never be bought second on her. I am not budging from that position.