My mother has dementia and sometimes does not recognise me. How can I care for her patiently?

Even as her memory fades, your loving care still reaches her heart and is still recorded as devotion with Allah. Understand that her confusion and difficult behaviour come from the illness, not from intent, so you do not take it to heart. The Prophet ﷺ said: “Indeed, gentleness is not found in anything except that it adorns it” (Sahih Muslim, Book of Virtue, Joining of Ties and Good Manners). Keep a regular routine and a safe environment, and follow the doctor's advice on her care. Take turns with family so you do not burn out. Remember how she once cared for you; now it is your turn to repay her with patience. See maintenance of parents.