How to deal with a grieving cat

Last week we had four cats. By the end of the week, we had one left. Our grumpy old neighbor had another poisoning spree. I wonder when he would change, that man. From what we've gathered, there were five casualties: two dogs from our neighbors and three of our cats. But what troubles us is the state of the one remaining. She is about a year old, still a kitten by age, and very close to her brother, mother and father, the ones who died. I believe when my father buried the carcasses, she wasn't around to know and sniff them goodbye. Now when we feed her, she always stops and looks around like she's expecting the others to come. She also cries differently and is constantly searching. It's very heartbreaking to see. So how do you help a grieving cat? Because I really wish she moves on sooner than later...

Coincidentally, I was reading London's White Fang and The Call of the Wild the time that our cats died. :(