Originally it had a 20 / 30 / 40 / 50 / 60 flat true damage for getting the third hit along with 4 / 5 / 6 / 7 / 8% of targets max health.
A lvl 1
has 518 health not including runes/masteries if
got the 3 hits off she would deal (if she had started with W) : 20 + (4% of 518 = 20.72) = 40.72
Same scenario with new setup: 6% of 518 = 31.08
Though she now also has a minimun damage threshold of: 40 / 60 / 80 / 100 / 120 (Note of % Max HP scaling: 6 / 7.5 / 9 / 10.5 / 12% of target's max. health)
This way it still deals less damage and isn't as punishing as the old scaling against a squishy target. The .72 of the older one might (I am very unsure though) have been rounded up at times. She is INSANE at busting Health tanks, but not so great against low health targets. Also there is the support which can help out the carry to lock her down and make her a quick meal for their carry.