Does the clear fluid that is discharged after masturbation during the daytime in Ramadan—the nature of which the girl was unaware of—invalidate the fast?

Your fast is valid, because the clear liquid mentioned is pre-seminal fluid (madhy), and its discharge does not invalidate the fast according to the preponderant opinion of the scholars. However, you must repent from masturbation, as it is forbidden in all circumstances, whether a person ejaculates or not.