The pilot reported that the tailwheel on her single-engine airplane had just undergone maintenance to alleviate a shimmy and was told to practice some touch-and-go landings to see if the problem had been alleviated. The pilot did several landings and said the shimmy had improved but was not completely gone. However, on the sixth landing, the pilot landed on the tailwheel, which resulted in an "extreme and violent" shimmy. The airplane veered to the right and the pilot tried to correct for it by applying pressure to just one brake. The airplane continued to veer off the runway, so the pilot applied both brakes and the airplane flipped over, resulting in substantial damage to the right wing strut and rudder. The pilot reported that there were no preaccident mechanical problems and that the accident could have been prevented if she kept the airplane on the runway.