Hi is there any medication that my wife can take to increase the size of the legs and thighs to make them a bit bigger?

See below. Best way to increase muscle size is through increased physical exercise targeting the muscles in legs/thighs. Physical trainer or bodybuilding friend can suggest which exercises to perform. Many exercise programs target those specific muscles, but should work whole body for muscle balance. Avoid using Anabolic steroids due to serious adverse side effects. Good luck.