It's hard to say goodbye

Our cat, Patches, will be 17 years old this November. Or would be, except we don't think she's going to make it through the week. 

She hasn't taken food or water for about 6 days, can't walk more than a few steps before laying down to rest, is noticeably thinner, and is hiding in a box of blankets in our basement. She can barely manage a "meow".

She's been with me since she was a month old (long before I met my wife), and is the stereotypical lap cat.

We're planning on letting our 6 year old daughter spend some extra time with her tomorrow morning, after which I'll be taking Patches to the vet. I don't think she'll be coming home with me though.

I'm surprisingly upset about all this.