Our kitten died at 10 weeks unexpectedly and I can't sleep because I'm worried about her sister. Advice?

I had a similar problem a little over a month ago when i took our little al to the vet to be neutered. He died immediately after the anaesthetic was administered. His little sister alfie was left behind. She was completely devastated, would not eat any cat food only the odd chicken leg. She is back eating now but is still looking for her brother. We were going to take alfie to be spayed but i dont have the heart at the mo. I couldnt stop crying for the first 2 weeks nor could i leave the house. You are under a lot of stress at the minute so please do take care of yourself.