Unless the body sits in more of an anatomically upright position during the *process of dying,* the majority of the blood will remain more central to the heart and visceral organs.
She died slowly (probably heroin or another opiate), as opposed to just falling over of sudden cardiac-death.
As the body systems shut down, they prioritize functions, and auto-regulate themselves. The heart's priority is the upper half of the body (i.e., vital organs and brain), so whatever oxygenated blood flow is still available stays in a more crucial area in order to preserve life until it just can't anymore.
And obviously the end result is death, and once the heart is totally stopped the blood will stay where the heart last pumped it...unless, of course, the body is moved before all the shit settles.
And there's a whole lot more in the upper half to putrify than there is in the legs, which are flesh and bone.
I'm calling bullshit.
She died before she could fully begin her metamorphosis into a lizard being, that's why her legs aren't green.