We've stayed there several times and yes, it is definitely worth checking out. Your room rate will depend on your sister's rank, but all rates are extremely reasonable for a deluxe quality hotel room located so close to the Magic Kingdom. You are also within walking distance to the Polynesian and the monorail.
We have never had an issue with room cleanliness or service, rooms are among the largest on property, and the food prices are more in line with "real world" prices then anything else you're likely to see in WDW.
Hope this helps, and enjoy your trip!