Medea is a conflicted character. She is torn between her feelings for Jason and her perceived duty to her father. Question: To what degree is she responsible for her actions?
The issue of whether or not Medea is responsible for her actions is central to understanding "Jason and the Golden Fleece." There are two possibilities. The first is that Medea is a puppet of the gods. In this case, "Jason" is really a story about how Hera exacts revenge on Pelias. The second is that Medea, while influenced by Hera, ultimately chooses to side with Jason out of love. In this case, "Jason" is about Medea's devotion.
The answer to this question hinges on whether or not the gods are irresistible. Dr. Rosenberg addresses this question in the introduction to the "Illiad." She indicates, "Even though the gods may give advice or help, a mortal's actions in response to any given situation are determined by his or her own personality and ability. Consequently, a mortal's fate is created by the interaction between personality and situation. Because the Homeric gods are not all-powerful, mortals can be dignified, morally responsible, and important. The world of ancient Greece contains no puppets" (123).
Let's look at the text of "Jason" to see if there is a reading that supports this view.
In fairness, Medea's love for Jason begins with divine interference when Eros shoots her with an arrow (180). After this, the relationship between the actions of the gods and of Medea becomes more complicated. On pages 186 and 187, Medea wrestles with the choice to help Jason or to remain loyal to her father. She becomes so distraught that she even considers suicide (186). Hera intervenes and renews her will to live. Medea, however, makes the choice to "save the man I love" (187).
Ultimately, Medea's own skills and talents enable her to aid Jason in his quest. She uses her magic to dismember Jason (191), her herbs protect him when he fights the bulls (193), and her spell sends the dragon to sleep (199). Without Medea's active, willful participation, the quest for the Fleece would have ended in disaster. In summary, I believe that while Medea is influenced by the gods, her most important choices remain her own.