Basically it goes like this :
All of the Passes include the parkhopping feature, as well as discounts on certain items and at the resorts
the most Expensive pass is the Florida Resident PREMIUM annnual pass which includes free parking at all parks and hotels,entrace to the four main parks (Magic Kingdom, Animal Kingdom,Epcot, ans Disney Mgm Studios) It also includes admission to Both water Parks (BLizzard Beach and Typhoon Lagoon) Disney Quest ( an indoor arcade/ similar to a Dave and Busters or Gameworks but better) and other perks that Im not exactly certain about but you can check on Disney's Website this pass has no blackout dates (you can go ANYDAY of the year)
Next in line would be the Florida Resident ANNUAL Pass which includes Admission to the four main parks, free parking, it basically takes away the option of waterparks and disneyquest, etc.
the last in line would be Florida Resident SEASONAL Pass wich works just like the ANNUAL pass except it has blackout dates, mainly the Summer Months, The week of Thanksgiving, The weeks Around Christmas and New years And the Weeks around Easter and Spring Break.
So If your sister lives nearby Orlando and will be visiting the parks alot during the summer of aroumd holidays it may be better to purchase either the ANNUAL or PREMIUM ANNUAL pass.
Hope I helped
Click Here for Disneys Page with all the Info