My daughter has a ganglion cyst. if you wait and do nothing will it go away in a year?

May be: Ganglion cyst , will some times disappears but not always, usually require surgical excision. Treatment with aspiration will not cure, real danger is possibility of infection into wrist joint. Hitting with a book is no no, will cause damage the adjacent structures.

Sometimes: Some studies on ganglion cysts show up to a 35% spontaneous resolution rate in children. If it is not causing any problems and is not getting larger then it is perfectly fine to observe it. Aspiration has a 50-75 % success rate. If done with appropriate technique infection is an extremely low risk. If the cyst is bothersome the most effective treatment is surgical excision.

Maybe: Some ganglion cysts can get smaller and resolve on their own. If their is no pain or severe dysfunction with hand use, one can wait and see.