Wheretogo,
Firstly let me clarify that I am not about to defend the US consul(s) who rejected your mother's visa application. However I now ask you to get in his/her shoes for a little while. A US consul on average has 45-60 seconds to make up his/her mind about a B-1/B-2 application. Let us look at the factors associated with your mother's application:-
(1) She does not have a job in India to "bring her back" to
(2) Her only son resides in the US
(3) She is alone in India (I apologise if that is not the case, but your post suggests that)
Now by law, every intending visitor to the US is deemed an immigrant. The burden of proof is on the applicant to convince otherwise. Now if you are a US consul and see an application from an unemployed middleage woman whose only son lives in the US, will you not be sceptical about her intentions to return to India?
I totally understand your frustration. In our (South Asian) culture parents are deemed very important and I can only imagine how heartbroken one can feel when government regulations stop us from having our parents come over to visit us and our kids. I have been lucky in this department since my parents are triple citizens like me and all three of my siblings are either Pakistani-Americans or Pakistani-Canadians, which translates to ease of travel to visit me in the US. However if that was not the case, I would have felt as frustrated as you (and others) feel.
I want to reiterate that my post was not intended to defend the action of the US consul(s), but just an attempt to portray their point of view.
I wish your mother the best of luck and hope she gets a visa soon to visit you in the US.