Hi, Elizabeth!
October is a great time to visit Walt Disney World, and the weather is usually ideal for swimming and water parks. However, I usually opt out of adding on the Water Park and More option.
Unless you plan to visit Water Parks at least twice, it is cheaper to just buy a 1 day ticket to your Water Park of choice than to add on the Water Park and More option. Other "options" include DisneyQuest or 9 holes of golf. Now I don't know your daughter, but guessing she would rather play in the Magic Kingdom than be swinging a golf club! And, at age 4, I really don't think she would get much out of DisneyQuest.
I do not know what resort you are staying at, but chances are you are going to have a nice pool area. We spend so much time selecting the best resort, then we are never there! What better way to enjoy your resort than to sit pool side for an afternoon!
If you plan to make several visits to the Water Parks, then it is worth it. But, if you think it will be a one day thing, just buy a 1 day ticket at the ticket window of the water park. That way, you will save a few dollars, and if you decide to skip the water parks completely, you have not spent a dime!
Enjoy your Fall vacation in Walt Disney World, and if your schedule permits, check out
Mickey's Not So Scary Halloween Party! Have a great time.