Sefer Halachot Gedolot 2, Laws of Kiddush and Havdalah, page 100

And women and slaves, even though sanctifying the [Sabbath] day has a time set for it, and it is accepted by us that women and slaves are exempt from all positive time-caused commandments, with regard to sanctifying the day, they are obligated. As Rav Adda bar Ahavah said (Berachot 20b): women are obligated in sanctifying the [Shabbat] day from the Torah. And Rabbah explained the reason: the Torah says “remember” (Exodus 20:8) and “guard” (Deuteronomy 5:12). All who are included in guarding also are included in remembering. And women and slaves, because they are included in the guarding of Shabbat, they also are included in remembering. [Translation by JOFA]