Enlarged Lymph Node

In December of 2004 my Mom was diagnosed with endometrial cancer, 54 white female nonsmoker not over weight.  She had a complete hysterectomy and 18 lymph nodes sampled. It was determined that her cancer was Stage IA, there were no signs of lymph node involvement and she would need no further treatment.  Last spring she began noticing some slight pain in her left hip and lower back that she attributed to a couple times she had slipped and over stretched.  After our dog (a boxer) jumped into her right side causing her to shift the pain became much more intense and eventualy subsided.  Over the summer she had all kinds of tests, x rays, bone scans, blood work and everything came back normal.  Physical therapy helped the problem some but never completely got rid of it.  A cortisone shot in September resulted in a fever and  intense pain for about a day or 2.  In September a catscan showed she had some swollen lymph nodes on the left and right illiac chains.  A biopsy came back negative.  Worried that the biopsy could have missed, repeated the catscan 6 weeks later, stable to the first one.  The catscan was repeated 3 months later and this time it came that a lymph node on the left external illiac chain had enlarged to 5.5 x 3.2 from 3.8 x 2.3 in November and another biopsy is now scheduled.  The oncologist is concerned that the lymph node pressing on a nerve causing the pain.  However, she has had this pain since May of 2007.  She is still having pain, while not extreme or unbearable it is enough to be an annoyance in her daily life and limit her activities.  When she complains that the pain is worse it seems o be the result of a specific event i.e., tripping, walking in nyc, etc.  A back doctor seemed to think that it is from arthritis.  Could the behavior of this lymph node and the pain be caused by anything other than a cancer returning?  She has no other symptoms such as persistent fever, weightloss or itching, she is tired but has always complained of being tired.