Did she get wet? A buddy of mine has a Trail Boss that would not rev after it went through a fairly deep puddle. It seemed as if the rev limiter kicked in (as in reverse). He tried pushing the button and that didn't help . . . he just let it dry and off he went.

It may just be the rev limiter. If your X has a circuit board look for the green wire that comes from the button (there should also be a grey\white and a lite purple one bunched in with it) and disconnect it from the board. This disconnects the rev limiter . . . if you bike then works fine either a replacement is necessary OR tape over the end of the green wire and have no rev limiter at all.