Need advice about radiation therapy for my mother

My mother (72 years old) was diagnosed with pT4b pN0 (Stage 2, moderately differentiated) colon cancer in April 2011. She had surgery shortly after, they removed a section of the descending colon (no colostomy bag) and removed 30 lymph nodes (pathology said all 30 were negative for cancer). She then started chemotherapy in June 2011. She was given the following:

FOLFOX level FOUR #6: Oxaliplatin and Leucovorin coctail w/ Fluorouracil stage delivered via portable chemo pump 2 days each session (~2 hrs), 12 days off rotating for 6 months.
PORT will be surgically implanted in her chest prior to chemo treatement for the duration of treatment protocol.

She did exceptionally well, no real side effects. She just finished her last chemo treatment in mid January 2012.
The issue is.....they want her to do radiation therapy to the abdomen (5days/week for 5 weeks) just because without any definitive "reason why" other than "it's recommended". My mother does not want to do it at all because of all of the side effects....and quite honestly I can understand that and kind of agree. My brother does not agree and insists that she have the radiation therapy, but it is ultimately her decision and she just can't figure out if she should and/or really needs to do it in order to prolong her life. From everything I have read based on her staging, surgery and chemo are all that are needed. It seems only more advanced Stage 2 (N1-3) or Stage 3 on that it's imperative for higher 5-year survival rate. As is, with no radiation, the standard 5-year survival rate falls into the 70-75% range. The question becomes, does the radiation really increase it? by how much? if not by much, then is it really worth going through it just for the sake of it? Also, we have to look at quality of life, if she's burned, blistered, sick (and more) from it and it does run risks of permanent damage to "other" areas/organs with non-reversible side-effects....is she just jumping from 1 frying pan to another? They haven't said "we didn't get all of it or there may be some left and this will greatly increase your chances of living longer". Does anyone have any advice or information or personal experiences to share?? We would greatly appreciate it!! Sorry the post is so long, just wanted to give the entire picture hoping to get advice based on the exact situation. Thanks!