Try this: run your knuckles with moderate pressure down her back parallel, to her spine, on both sides of her spine. Pay special attention to the places your saddle tree touches and areas prone to ouchy-ness -- e.g both sides of the withers, the loin, the lowest part of your horses's back. Observe the results. Did she move? Pin her ears? Shake her head? Did her back muscles shiver? Did she duck down? Turn her head to look at you?
Those are all signs of discomfort. Sometimes a horse's reaction is slight and sometimes it's very apparent. Sometimes it's nice to have a second person watching your horse for these signs.
Just because she doesn't react to this test doesn't mean there isn't a pain issue. A chiro might be able to help. Does your saddle fit? Are you a light and balanced rider? There are so many reasons for acting out undersaddle. Before you brand her as bad, make sure there isn't a health or pain issue that makes working uncomfortable.
Last edited by Brighteyes; 11-24-2012 at 11:04 PM.