(1) Background: Anorexia nervosa is an eating disorder (ED) where up to 30% of individuals remain unresponsive to treatments, whether they partially respond, or do respond and later relapse. It has been broadly reported how presenting maladaptive family functioning and communication style contributes to treatment drop-out, poor treatment compliance, and poor long-term outcomes. We studied the mother and father of a patient with AN, binge-purge subtype (according to DSM-IV TR) who achieved remission after her parents but not her attended an intervention through a psychotherapy group for parents (PGP). (2) Methods: We previously reported this patient’s case report, and now, through an Interpretative Phenomenological Analysis (IPA) approach, we aimed to explore the understanding and meanings ascribed by the mother and father to their experience at the PGP and to their daughter’s clinical and functional improvement. (3) Results: We identified two main stages along the process: one related to the presence of maintaining factors of their daughter’s disorder, and the other related to the emergence of a reflective function and to the implementation of behavioral, emotional and cognitive changes. (4) Conclusions: The interview revealed both parents’ experience at the PGP promoted a change process, where they were able to modify their previous style of communication and functioning, and to identify them as a contributors to maintain their daughter’s disorder. Reflective function (RF) emerged in the mother and father throughout the psychotherapeutic process. Both parents also revealed some elements that were intergenerationally transmitted, that affected three generations and contributed to maintaining the ED. We observed the multilevel open-group structure of the PGP, enhancing the mother’s and father’s change process.