Is it permissible to fast the six days of Shawwal before making up for the missed days of Ramadan due to menstruation, and can they be counted as part of the make-up days?

Scholars have differed on the permissibility of observing voluntary fasts before making up the obligatory fasts of Ramadan. The preponderant opinion is that it is permissible and valid, even though it is more befitting to make up the Ramadan fasts first because they are obligatory.