Hi Alisa,
How wonderful that you and your sister are going to Walt Disney World with your mother for her retirement. What a great way to honor the milestone, and I'm sure that you're going to have a memorable trip.
Although most of February is typically a less crowded time of year at Walt Disney World, you are going during Presidents' Day week which means that the crowds will likely be high as many people visit that week. That week will be quite busy as compared to September when you are used to coming.
However, there are great tips for making the most of the park when it is crowded. I always recommend getting to the parks as early as possible, even about 30 minutes before the scheduled opening time if you can, as they are typically less crowded first thing in the morning. If you are staying at a Walt Disney World resort, be sure to take advantage of Extra Magic Hours, which allow guests staying at a Walt Disney World resort to enter a particular park early or stay late on specific days. Also, if there are any restaurants that you and your family would like to dine at, be sure to make Advance Dining Reservations so that you are not disappointed by not being able to get a table. You can do this by calling (407) WDW-DINE (407-939-3463) or visiting the
Disney Dining reservation site.
At the time of year that you are going, Epcot's crowds should be fairly consistent throughout the week and weekend. I don't see a need to avoid Epcot on the weekends during your trip. I find the website touringplans.com to be very helpful for forecasts of future crowd levels at the Walt Disney World.
Have a wonderful trip, Alisa, and please do not hesitate to ask if you have any further questions.