Answered by Ustadh Abdus Shakur Brooks
Does a woman need to make up voluntary fasts if they were interrupted by menses?
She does not have to make up her voluntary fasts because the general rule in the Maliki madhab concerning those who must make up voluntary fasts is “nullifying voluntary fasts purposely without any valid reason or excuse necessitates the obligation of making it up”. This excludes those who were forced by compulsion to nullify their fast or those who forgot they were fasting, and those who were interrupted by matters such as menses and postnatal. Such people are not obligated to make up their voluntary fasts because either they did not nullify their fast on purpose [ such as a person who ate out of forgetfulness] or they broke their fast on purpose but due to a valid reason or excuse [ such as compulsion, or menses and postnatal].
source : http://mathabah.org/2009121290/maliki-fasting-sawm/does-a-woman-need-to-make-up-voluntary-fasts-if-they-were-interrupted-by-menses.html