3 women is an allegory about....
growing up and accepting change. In my opinion that is. I believe that each of the 3 women is a symbol of a different stage of womanhood. Pinky the child, Millie the adolescent/20-something, and Willie the expectant mother. Where my opinion differs from others though, is that each of these women is slowly growing out of their stage and is reluctant to move on. Well, at least Pinky and Millie are. Pinky is far too old to be behaving the way she does at the beginning of the film, and is in dire need of a change. The same with Millie. She is stuck in the stage of the flirty adolescent girl and is reluctant to move forward. Willie is the acception. She is where she needs to be in life...she is the appropriate age for bearing children.
When Pinky awakens from her coma, her change occurs. She is jump-started and leaps from childhood to adolescence. Millie, horrified from these changes, slowly morphs into a more motherly figure. She becomes more like Willie and her reactions are akin to those a mother feels when they realize that their child is no longer a child, but a young adult.
When Willie's child dies, it affects Millie and Pinky. Pinky, frightened by the promise of motherhood to come, reverts back to her childlike state again. Millie, coming face to face with the same horror, realizes that she must take her place in the world as a caring mother to Pinky. And Willie, being the only one who has accepted her role from the beginning, becomes a grandmother to them both, leading them both through their changing stages of womanhood.
I also believe that they murder Edgar. The death of Edgar is a metaphor for women breaking free from the distraction that is man. Men affect the women all throughout the film. Millie is kept from growing up because she is constantly waiting for the one man to come who will love her. Willie is locked into an unsatisfactory situation because she is carrying Edgar's child. When Edgar died/is murdered, the women are metaphorically freed from men and all the distractions that come with them, and are completely free to embrace their destiny's as women.