My sis has PCOS. Was on femara (letrozole) CD5-9. 2 follicles got matured, at CD11 got pregnyl injection. Is there a chance that egg still did not release?

Yes possible. Many PCO patient have issues not only with follicle stimulation, but ovulation as well. There is no guarantee that she ovulated. I would recommend she use ovulation prediction kits to give more information. They are available next to the pregnancy tests at the pharmacy.