Just let your mom try again,

give us a break, please. She will get her visa sooner or later. Just try again. Go to American embassy's website, they have clear explanation why they reject parents' visa. All those who stay in U.S. for a long time, can't make the VO believe that they have strong ties to China, otherwise, they won't overstay. Got it?

But she still has a chance, just keep trying. GL.