What Monaghan points out is that there is also a form of belief that looks to a fourth figure in the Feminine. As so quaintly put by Cybill Shepherd it is the "Cheerleader".
Typified in archetypal psychology this tri-part becomes a quartet of: Mother, Amazon, Hetaira, and Medial Woman/Medium. The inherent problem with this version is that these labels can be strict and restrictive. The Amazon/Maiden concepts don't always go together, neither do the Medial Woman and the Crone.
Monaghan instead presents the quartet of: Mother, Daughter, Lover, and Crone.
The Mother is the traditional nurturer and giver of life, but also figures into the cycle's ending. For if there is a birth, there must later be a death. She is the mother of plants as well as beasts/animals and represents the bounty of the Earth.
The Daughter is the young woman, one who is not involved with a mate or sexually active, but rather contained within herself. She is also strong in her own right and often is shown as an athlete or warrior, but she is still young and needs protection.
The Lover offers connection to all things, ourselves, others, and the Divine. She implies passion and love, as well as the sexual nature.
The Crone brings lessons of wisdom and connection to/for the greater good. While she is introspective she does so out of service and is self-less and meditative.
