What is the expiation for someone who committed zina during the daytime in Ramadan and repented, knowing that she is unable to fast due to a chronic illness, there is no slave to free in our time, she is not married to ask her husband, and her family is well-off?

You have committed a great sin by intentionally committing this indecency during Ramadan, and you must repent sincerely. Scholars differ regarding the obligation of expiation (kaffarah) upon a woman: some do not see it as obligatory, in which case you are only required to repent and make up the day. Others see it as obligatory—which is the more preponderant opinion—so you must fast for two consecutive months. If you are unable to, then feed sixty poor persons (one and a half kilograms of rice for each poor person). If you are unable to feed, then the expiation falls away from you according to some scholars, and this is what Shaykh al-Islam Ibn Taymiyyah and Shaykh Ibn Uthaymeen preferred. If you expiate when able, it is more cautious and a way to avoid scholarly disagreement.