Fiora builds 2 offensive items and rest full tank

Assuming her ultimate she would need her passive to do 20% max hp true damage. She would need 378 bonus AD to reach 20% max hp true damage. The highest AD items are Sword of the Occult (110 AD at max stacks), Maw of Malmortius (95 AD if below 30% health), and any of the items that build out of BF sword (80 AD). She could get a MAX of 205 bonus AD assuming 20 Sword of the Occult stacks and being below 30% health with a Maw of Malmortius. Which...is still half of what she would need to do that much damage.