Arthritis or Tumor?

Hello,
My dog is a 13 year old boxer the under went surgery and radiation for removal of a meningioma tumor last July.  The tumor was at the base of her skull by the 2nd or 3rd vertebra.  It affected her left side and since removal she is has done remarkably well (everything is normal).  However, she does have arthritis and now she is showing signs of difficulty walking with her hind legs and she has had excessive panting and is drinking water as if she was on prednisone.  She does not appear to be in any pain as her behavior is puppy like and very normal, and her reflexes are responsive.   Do you think her issues are tumor related, if not is there a good alternitive treatment for arthritis. At this time she is taking deramaxx but due to a pre-existing pancreatitis condition I am fearful of upping her doseage from 25 to 50mg.  Posie is a very small boxer and weighs 46 lbs.  I am very curious about acupuncture and your thoughts on it.
Thanks
Diana & Poise Mae