She may very well have something called Ehlers Danlos Syndrome (EDS)
My daughter has this, it is rare 1 in 5,000 have it.
People with EDS have faulty collagen and are very lax in their ability to bend. They are VERY flexiable and used to be the ones in the cirus that were called contortists. (the ones that could fold and bend their bodies into small boxes)