12 year old GSD with mammory tumor

Please forgive the cross posting, but I am posting to breeds and behavior
groups too since I know that not everyone checks out the messages on the dog
health newsgroup.

Our much beloved 12 year old German Shepherd, Josey, had a mammary tumor
removed a week ago. She tolerated the procedure very well and is healing
quite nicely. However, today the biopsy results indicated that the tumor
material was cancerous. The vet said that he got "clean margins" around the
surgical area and that her lymph nodes do not appear to be enlarged.

Factors: She has always been a healthy active dog, but has slowed down a
lot during the last six months. She has been diagnosed with mild DM, which
has just now started to give her some minor trouble with her right rear leg.
Her senior exam bloodwork revealed that she probably has the beginnings of
Cushing disease, but no symptoms have appeared yet. She still goes up and
down the stairs pretty frequently, but is starting to have trouble holding
her bowel if there is "a round in the chamber".

Josey is still happy, eating well and really enjoys going swimming a couple
of times a week. We go for short walks rather than long ones these days.
She shows no signs of discomfort at this point.

My vet is going to talk to me about chemotherapy today. My question is, is
it worth it? I love this dog with all of my heart and want to do right by
her. I know that we are lucky to have been blessed with her for 12 years of
good health. Being that I am involved in rescue, I have heard from many,
many folks who have lost their pets at much younger ages.

I want Josey to have a wonderful life, and not be wracked by side effects of
Chemo. If she has limited time left here on earth with us, I want her to
enjoy it.

Any advice from those out there who perhaps have been through a similar
situation?

Yours in dogs and rescue,

Lea S
Sterling VA
www.shepherdrescue.org