It probably depends a lot on your mom and how well she is able to travel, navigate crowds, what she wants to do, etc. How old is she?
We normally do 5 days in the park with one day off in the middle for DTD and hanging out at the hotel (we usually stay at the DLH), usually do half a day at the pool, which may not be something you want to do in January depending on weather. It's nice to have a day for a break in the middle of 5 park days, which can be a lot. Three days is not uncommon for many people.
Have you talked to the mom about the trip so you know what she wants to do or what her energy level might be at the parks? My mom would be no more than 2 days and done, probably not even two full days, but it really depends on her.