On erev Purim, there is a custom to give three coins to charity, to recall the half-shekel that was donated annually to the Temple treasury in the month of Adar.
“[Women are exempt from the mitzvah of Machatzit HaShekel, yet there are reasons for them to perform it. [One reason] is brought by… Reish Lakish (TB Megilla 13b) who connects the half shekel donation to the story of Purim, and taught that while Haman solidified his plot against Israel through his donation to Achashverosh’s coffers, Israel was protected by their donations of shekels to the Divine service.
…our modern half-shekel donation is in memory of this protection. Therefore women are obligated in this custom based on the principle of ‘they were part of the miracle’.
Purim is a time of giving. For those of us women who are blessed with sufficient funds and the ability to do so, it is a great time to contribute our part to support our community, financially and spiritually, and donate zecher l’machatzit ha-shekel.”