How is sincere and complete repentance to God possible after feeling remiss in patient care, and some of them died due to ignorance of medicine, despite having a pure intention to help them?

It appears that the questioner caused the death of patients due to her ignorance of medicine and her shyness about asking questions. Therefore, she is liable for her error. Whoever practices medicine without knowledge or expertise is responsible for their error and their deliberate actions, as the Prophet, peace and blessings be upon him, said: "Whoever practices medicine without being known to be a physician is liable." What is incumbent upon her, along with repentance, is the expiation for accidental killing, which is the freeing of a believing slave. If none is found, then fasting for two consecutive months. And her aqila (male relatives on her father's side) owe the diyah (blood money) of the deceased, unless the heirs forgive it.