Karen,
You said she's a 1yr-old-pup and active, but does the 50 pounds include a bit of extra weight or is it just solid muscle? Even a young, active dog can have too much meat on the bones, and if she's part terrier, her natural body make-up may be on the smaller size than a full Golden.
And since she's a new dog to you, have you had her tested for heartworms? I found this link, which may or may not be helpful: Rapid Respiration in Dogs.
I agree with Velobambina -- the best and most thorough way to see if Lucy is truly healthy (looks can deceive) is to have a thorough exam, including x-ray. It can be costly, but you'll know. She also may have been injured or sick in some way prior to you getting her, which may be affecting her breathing somehow (fluid in the lungs, etc). The x-ray may rule that out, too.
Either way, I'd check it out with a good veterinarian.
Best wishes to ya & hugs for Lucy,
~BikeMomma
Last edited by BikeMomma; 11-04-2007 at 09:48 AM.
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." --Albert Einstein