I don't see you writing what other drug you have in mind.
Postoperative and chemotherapy patients are cared for by a team of specialists who select the appropriate therapy for a particular patient. Certainly, the doctors who take care of your granddaughter, after assessing her health condition and disease entity, applied the treatment that is most appropriate for her. I also suspect that possible treatments have been presented. You should get information about the prognosis after the treatment from the specialists who are treating your granddaughter.

For my part, I am attaching the scientific publications I have found that may be of interest to you and give you an overview of the disease and treatment: In the first study, studies were conducted describing the role of staging and adjuvant chemotherapy in adult patients with overt, immature stage I ovarian teratoma after fertility-conserving surgery. The conclusions were as follows: Adult patients with pure immature stage I teratoma had 98.7% overall survival, and the recurrence rate after fertility-conserving surgery was low.

Link to publication: https://ijgc.bmj.com/content/30/5/664

The second is a literature review on the diagnosis and treatment of immature protozoan. It gives an overview of the types of cancer and the different methods of treating them. In the conclusions, it can be noted that the treatment depends on the type of cancer, and accurate diagnostics is required when selecting the appropriate therapy. I am attaching a translated excerpt from the conclusions of the review "Immature teratoma is a rare malignant germ cell tumor and it is the only such tumor for which we have a tumor classification among germ cell tumors and for which, although we do not have a consensus on the treatment of the pathology, it gives a good therapeutic outcome, along with good survival rates and a high degree of fertility preservation. Additional studies are needed to clarify the need for chemotherapy, especially in pediatric oncology. Surveillance is preferred, given the adverse effects of chemotherapy. Possible alternative, targeted treatments also hold the future. These efforts are necessary because of the age at which these malignancies appear and the potential to cure the disease. Particular attention should be paid to genetic mapping of histological fragments in order to stratify the patient's risk based on its importance in prognosis and future treatment."

Link to publication: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10177811/