Time for euthanasia?

My dog Juliet is 12 1/2 years old. She is a black lab with Addison's disease which has been well controlled for many years. She is currenty on Florinef (0.1 mcg - 5 tablets twice a day and on prednisone 7 1/2 mg. / day).

She also has severe arthritis of the forelimbs (elbows). She is on metacam once a day, and earlier this week I took her to the vet and he injected her elbows with hyaluronic acid and cortisone.

Last summer she developed a neurodegenerative myelopathy, which began with weakness of her back legs, and she is now unable to walk more than a few steps. I bought a rear-leg wheelchair for her last week, and have been trying to accustom her to it, after asking the orthopedist to help fit it properly. However, she doesn't seem to be able to walk in it. I know that it can take time for dogs to accustom themselves to the wheelchair, but I think that her elbows are still too painful when she walks on it. She won't take more than a few steps, then her legs start to shake and she won't move.

When she isn't using the wheelchair, she can, with help, ascend the steps to the house (13 steps), and even go up the back stairs, which are wider, by herself, though slowly.

She is not yet incontinent, but I am wondering at what point the decision should be made to have her euthanized? She still wags her tail when she sees us, and eats well. But I don't want her to suffer, and I don't know how much she is suffering (when she was diagnosed with Addison's disease, a few hours before she went into shock and almost died she was still looking cheerful and wagging her tail, even though she was in renal failure).

She also gets recurrend UTIs, and when she gets them, she begins to vomit, and needs extra prednisone.

My family has plans go to go Hawaii in March. Up until now, we have had someone I trusted to keep an eye on her. That person has passed away, and I think it would be too hard to have Juliet in the vet for the week we are gone. I am also concerned what will happen if she becomes ill, or dies that week. I will keep looking for someone to care for her when we are gone.

How does one know when to end their dog's life? I always thought I would never consider euthanasia, but I am now wondering if that is the best thing for her.

Sincerely,
Katy Broner

Dear Dr. Marie,

Thank you so much for your advice. I was wondering: she is such a cheerful dog, that it's sometimes hard to tell. Her tail is almost always tucked between her legs (has been for over a year now), but she does wag it frequently. She seems to like company, but not being touched too much. I always said that I would never euthanize a pet, but now I'm so conflicted.

Sincerely,
Katy Broner