I can speak to the management of the ovarian cyst
. You didn't give a description of the cyst
beyond its size, however, common things being common it is quite likely your daughter has what is considered a functional cyst (i.e., a physiologic cyst that forms due to the ovarian response to its hormonal environment), or a corpus luteum cyst (i.e., the normal cyst that forms after ovulation). A functional cyst will appear simple on u/s, while a corpus luteum will appear complex.