While the Morton's neuroma was present before the show, it became increasingly more painful. This is a common condition for dancers. Dancing, especially for women, requires the use of certain footwear, which are most commonly high-heeled and narrow. Add to that the amount of time that a dancer spends on the ball of the foot, which also increases the pressure and the inflammation of a neuroma.
A Morton's neuroma is an enlargement and inflammation of the nerve that travels between the metatarsal bones. The pressure of the metatarsal bones causes the nerve become inflamed and painful, resulting in pain in the ball of the foot that often shoots into the toes.
I'm sure Jennifer had tried more conservative treatments, such as custom orthotics, before pursuing surgery. No doubt, she also had injections of cortisone during her time on Dancing with the Stars to decrease the inflammation. She may have even used extracorporeal shockwave therapy during that time also. Surgery to remove the neuroma, however, is a suitable last resort and she will undoubtedly feel significant relief.