Why did my cat die?

Hello,

The other day, our cat Misty (she would have been 16-years-old next month) vomited on the floor. It looked different than normal - it was more liquid and yellow. After that, she laid down right there and since then, she hadn't been able to move on her own. Her left back leg didn't even twitch the slightest bit the days following that. When she tried to walk on her own, she was extremely slow and that leg would just drag on the floor uselessly. She stopped eating and drinking, and she didn't even go to the bathroom. We put her in the litter box, but all she would do was slump in there and lay down. We left her there for 10-15 minutes, and when we checked on her, she still hadn't done anything. We gave her food and water, but she wouldn't even touch it. Her nose got this yellowish tinge to it, and her mouth became darker (not pink - it had a more blackish look to it). Her eyes became distant and foggy with an almost glazed-over look to them. We would pet her and she would purr a little - though nothing close to what she used to do. As soon as we stopped petting her, she would meow and continue to do so until we pet her again.

Last night, our beloved kitty passed away. Today, her nose began pouring out a little blood (we were unable to bury her yet, seeing as we hadn't been able to purchase something for her body until the next day). All I wish to know is what this sounds like. What was the cause of her death? Was it simply old age? Perhaps it was something to do with liver failure?

Please help get me and my family some closure as to the cause of our cats death.

Thank you so much.