What should a relative of mine do who did not pray in the hospital after undergoing a uterine operation and was prevented from moving due to the devices connected to her body?

Your relative erred by abandoning prayer after her surgery, for prayer is not to be forsaken as long as one's intellect is present. She should have prayed while lying down, even if without ablution (wudu') or dry ablution (tayammum (definition)) or facing the Qibla (definition). She must now make up the prayers she missed, along with repentance and seeking forgiveness, and resolving not to return to such an act. She is obligated to make up the prayers immediately in their proper order (Fajr, Dhuhr, Asr, Maghrib, Isha) for each day she missed. If praying them consecutively becomes difficult for her, she should pray what she can, then rest and complete them. Sheikh Ibn Uthaymeen was asked about a sick person who missed obligatory prayers, and he replied that all of them must be made up at once, in imitation of the Prophet, peace and blessings be upon him, when he made up the Asr prayer at Al-Khandaq (the Battle of the Trench).