What is the ruling of Islamic law regarding the past prayers and fasts of a girl who masturbated out of ignorance of its unlawfulness and its invalidation of ritual purity, knowing that she was unaware of the existence of semen for women?

There is no sin upon one who masturbates out of ignorance. As for fasting in Ramadan (definition), you are not required to make up the days if you are not certain that semen was discharged. And if you are certain, you are still not required to make up the days due to ignorance. As for prayer, the majority of scholars hold that it is obligatory to make up prayers if they were performed without purification. However, Sheikh Al-Islam Ibn Taymiyyah holds that making up prayers is not obligatory for one who omitted a condition or pillar out of ignorance. Based on the view that making up prayers is obligatory, if you are certain that semen or prostatic fluid was discharged and you did not purify yourself, then you must make up the missed prayers by estimation and diligent effort.