I'm having unusually hard time grieving

It's not as serious as other posts here, but I am struggling with immense grief.

A year ago, in August my family rescued a kitten. She was the tiniest, most precious being I've ever seen. Over the months I watched her grow, become curious with the world, develop her personality. Maybe it makes me a bad pet owner, but I love her more than the other two cats we have. She was calm, never mischievous, just the sweetest, smartest, cuddliest baby girl.

She had some health issues when we took her in but it was nothing serious as she quickly gained weight and strength. She started playing with other cats and seemed pretty normal. The only issue was her kidneys were a bit underdeveloped so she had to take meds regularly.

On Wednesday she got sick. We got her to the vet and the examination showed that her kidneys were so deteriorated they were almost gone.

Yesterday we said goodbye and decided not to make her suffer anymore.

I usually take grief pretty well. When people in my life passed away I was able to think logically and support others through it instead of breaking down. I'm autistic, so sometimes I'm a bit disconnected from my emotions, but this time it's very different.

I feel like my whole world collapsed. I'm trying to force myself into being productive, but it's hard to even operate my body. Life feels like I'm playing a first person point of view game, but the controls are broken so i can just sit and look.

I thinkit may be the fact that she was so small still. The world just seems really unfair and unreal right now.

I don't know what to do.