If you haven't found the cat's body, then there is still a chance that she is ok. I've had a cat not coming home for something like four days and then coming back and acting like nothing out of the ordinary has taken place.
Yeah my cat started disappearing for days - turned out he had decided he liked the neighbours house better cause they had cat food and dog food out constantly... He was one greedy cat. Hopefully you kitty will come back.
Update: she didn't actually kill my cat. But after I told her I knew she messed with my cat next day she appeared. So maybe she just kidnapped her, but I bluffed in time that I knew. This evening when the cat came home she vomited. So she gave her something bad, because she looks kinda sick. What the hell?
I am thrilled about the fact that your cat is back! I am happy for you.
I was going to mention to you that chances are that your neighbour is innocent. The most likely reason for a cat not coming back is that the cat got run over by a car. When you let a cat be outside, the cat's life is in fact richer/more interesting. But the downside is that the cat's expected lifetime is going to be shorter.
I learned this the hard way. At first I would walk with my cat on a leash. He absolutely hated it and eventually we let him out without a leash. At first he always stayed in our backyard, but then he began exploring more of the area. He would be gone for long stretches of time multiple times, and he always came back.
Until one day (after 7 years of taking risks), he hasn't. We put signs up, and people called us to tell us that they've seen his body after he got run over... My dad died at the age of 47, and my cat's death was almost more traumatic than my dad's death, as I felt responsible for the cat's death.