Cocoa the ratty (frank discussion of euthanasia, be warned)

I made the decision yesterday that it was time to euthanize my rat Cocoa, one of Fudgey's babies. She's had a bunch of mammary tumors growing for awhile and they finally got to the point where she was having a really hard time getting around. She still had some perk in her. When I got her out of the cage yesterday, she was trying to check out everything in the near vicinity and munching on raspberries. I'd been trying to decide what to do for awhile and I'd been really dreading euthanizing her. It would have been an easier decision if I had my great, awesome vet close by, but he's up in Mass. I knew I was perfectly capable of euthanizing her myself, at home, but euthanizing a pet is a whole different story from euthanizing research animals. I did some research and came up with the simplest, calmest method of humane euthanasia (carbon dioxide poisoning). I got everything together and meant to do it yesterday, but by the end of the day, Josh and I just couldn't bring ourselves to do it.
Tonight when I got home from work I got Cocoa a treat of black raspberry crisp and ice cream and fed her the ice cream as a last special treat. We got her all set up, gave her lots of pets and then slowly anesthetized her before finally ODing her with the carbon dioxide (made by reacting vinegar and baking soda). It seemed like a really peaceful way to go...she pretty much just fell asleep and didn't wake up. As hesitant and sad as I was to think about euthanizing Cocoa, once we got started and actually did it, I felt a lot better. It's nice to know she's not suffering and she didn't get to the point where she was in lots of pain or anything. We buried Cocoa in the garden along with Fudgey who had been resting in peace in the freezer since her winter time death.
I let Mocha see Cocoa's body before we took her outside. I'm most worried about how Mocha will cope with now being the only rat. She's never been particularly friendly with humans, so I'm wondering if she'll be more friendly now because she needs companionship. I've heard of that happening with other wild/mean rats in their old age. She's 2.5yrs old, which is elderly for a rat. She's still in pretty good shape though. She has a tumor on her ear, but it's harmless and doesn't affect her mobility or anything. Since she was spayed in an attempt to tame her, she will most likely never get any of the mammary tumors that doomed Fudgey and Cocoa. I guess only time will tell how she reacts to being alone.