I recently lost my kitty who was 17 but I had for 15 years of that because she was a rescue and I got her when she was around 2. When she passed away I bawled for days on end. She was my baby.

Now I've adopted another kitty who, it turns out, has a serious heart condition, but that's another story.

What has helped me:

1) Keeping a journal for and to my kitty. It's also a scrapbook with pictures and the condolence cards from the hospital where she passed away and my regular vet, etc. I write to her almost every day telling her how I'm doing with my mourning and saying how much I love and miss her.

2) I adopted another cat. This has helped my mourning the other beloved kitty considerably. I got him only a little over a week ago, and already adore him and I think he's very happy here. I have not at all forgotten my other kitty and still write to her regularly, but another cat in my life has helped so much.

Also, re hiding, I do think they can hide when they are dying, but vets have also told me that they hide when they're uncomfortable/in pain (not necessarily dying). In the wild, showing pain/disability could cost you your life, so they often don't show it and hide to be safe. If it were me, I'd sit or lie on the floor by the bed and keep her company for periods of time. She may not want to be pet right now, but may well like the safe company of her mama.

I didn't read the whole thread so I'm not sure if you're already doing this, but I'd consider regularly giving her strong (narcotic) pain medication. I'm sure your vet would be happy to give it to you. The only downside is that because it's a controlled substance, they only give you a few days' worth at a time and you have to keep going back for it.

When she does pass, I would ask the cremation company for a lock of her fur, if they do this. Where I live they offered it and it has been painful to look at, but also comforting to feel her with me.

Best of luck. I know how incredibly painful this is.