My elderly rats quality of life?

HI guys, please only answer this if you know what you are talking about and aren't some idiot that spends their time scrolling through rat questions so they can leave answers like 'eww rats, kill em'.

Anyway, so my elderly rat ebony lost her cage mate i'd say about a month ago now. She was obviously sad for a while but she knows what happened as i found her cuddling her sisters body one morning. I don't want to introduce her to new rats as i think this will cause her stress and she is already three. She'll eat as you'll see in the video, and drink too although she doesn't eat much but this is probably because she doesn't move so much anymore.

hen i don't have her out she just lies in her house most of the time, although she does come out sometimes and even climbed on the bars yesterday to see me.

But sometimes she lies out of her house and it looks like she's going to fall onto her side, some mornings she has A LOT of porphyrin around her nose but not always. She's on my lap right now and i can see she had large patches of hair missing, and her skin is dry and flaky although i feed her what she needs an not too much protein so i don't know why this is?

Oh and the other day i found her buried under some blankets in her house, led our on her side, in the kind of position i have found other elderly rat to have died in. I'm so worried, her breathing has also gone down hill and she sneezes a lot.

I'm so worried i don't know whether or not to keep her alive and see what happens (she still even wonders around my floor and explores) or to have her humanely euthanized.

She like me to handle her so i don't know if she is in pain but i do know that rats mask their pain well...i think i've got so worried that i'm not looking at it logically anymore and so i need another rat owners point of view. She has no tumors at all (well any external ones, i don't think there are any internal ones.)

Sorry this question was so long, but i would reallyyyyy appreciate anyone to help me out here. Thanks so much

this is her: http://www.youtube.com/watch?v=_41kKhcHvN4&feature...