It's probably the face; prominent cheeks, roundish head, button nose, large expressive eyes, appealing curves and reverse curves, being a cat (the internet loves cats, this is a fact)... all that good crap.
Phew! The changes are quite subtle; I had to go back and check the differences!
Probably the part that sticks out most to me is the ears, and I prefer them this way. Without casting aspersions I've always seen the big, droopy cat ears as a very anime feature but I feel these are more in the spirit of Sarah.
Heh, well there's not much more I can change without her becoming totally different. I do appreciate you actually checking other the older models, though!
Oh yes, the ears. With them up like that, she's around 20% more perky-looking. They're not big and hard to manage like before either (previously, I often opted to only draw one visible ear from profile or 3/4 view).
It's kind of cool that you mention Sarah's spirit. Having her essence alluded to makes me feel like I might be doing something right with her!