What should a girl do concerning her past prayers after recently learning about احتلام (wet dreams) and مني (seminal fluid)?

A wet dream during sleep does not necessitate ghusl (ritual bath) unless semen is present. Doubt about its emission does not obligate ghusl. Therefore, if the questioner is not certain that semen was discharged previously, her past prayers are valid, and she does not need to make them up. However, if she is certain that she prayed without ritual purity, then she must make up all missed prayers, which is the view of the majority of scholars, though some say making them up is not obligatory.