Where did it say in the article that she is illegal? Do you have a quote?
sorry for the delay on this - no quote, but the article made a special point about mentioning that the sons came over first, became citizens, got their degrees and then brought their mother over - and that she was able to get a job with benefits. I’m assuming that they would have also mentioned that she became a citizen if that was the case.
just did some more research - according to http://www.nytimes.com/2011/03/04/us/04immigrant.html she’s a “legal immigrant” but not a citizen.