I think that it is important to keep in mind that the actions of Devi Sita are ones of a Goddess. It might be difficult to fully judge the perceptions of the divine. It is important to recognize that in this light, our assessment of the divine might be a bit on the challenged side.
Certainly, in arguing that Devi Sita's feelings of disenchantment are justified in regards to her denunciation, one would point to the telling of the narrative that involves how she asks Mother Earth to swallow her. This helps to bring out how Devi Sita feels that she cannot overcome the ignorance of human beings, the citizens of Ayodhya who doubt her virtue. It is they who ask Lord Rama to test Devi Sita. Lord Rama being a great ruler who understands the need of leadership to be responsive to the needs of the people. Certainly, this can be considered to be a part of her feelings towards her denunciation. On some level, there is a gap between how she feels about Lord Rama and how she is compelled to prove herself. She does so, willingly in order to adhere to her dharmic conception as wife of Lord Rama, yet in seeing how the Earth swallows her, one can sense some level of disenchantment towards her denunciation.
On another level, it can be argued that Devi Sita's reaction towards her denunciation represents one of the heights of Hinduism's tenets In the Earth swallowing her, Devi Sita might be embodying renunciation of the world and not denunciation of it. A major idea of Hinduism is that all life recognize its transient nature and that there is no attachment to what one perceives. The ability to renounce the world and be detached from sensory perception is a key component to understanding the true nature of existence. Devi Sita does not exact revenge for what she endures. She does not become an avenging angel, or one who demands a sense of compensation for what she has endured as a woman and as a wife. She goes into the Earth as an action of detachment. Devi Sita has achieved a level of liberation that even Lord Rama does not fully achieve until later on in the narrative. In this, one can view her actions in a different light.