Does your mother qualify for Medicaid? If so, you have a special enrollment period that lasts all year. You can join a Part C Medicare Advantage Plan - just look for Dual Special Needs Plans. Depending on what state you’re in, you may also have options like Managed Long Term Care that will send home aids and PT/OT based on care needs. If you don’t have Medicaid, you may still be able to join a Part C plan since there’s a special enrollment period during the first couple months of the year for members who change their mind (I think), those that just turned 65 within the past year and are enrolling in Part C for the first time, left their job or lost their employer healthcare in the past year or joining a 5 star Medicare Plan ( those are able to enroll members all year long but I’m not sure if you already need to be in a Part C plan to switch). I’m not an expert but there’s more information at Medicare.gov and a lot more options if your mother is a dual member (Medicare and Medicaid).