First let me say that the Tree House Villas are GREAT!!!
Our family was there during the January 2010 cold spell and rain. The layout of the villa is perfect. The addition of the extra bedroom was perfect for our family.
Now it was cold and rainy so the extra wait stop was not that fun but in NORMAL Florida weather we would have just walked to the normal SSR bus stop and not rode the transfer busses.
If you could add the Boardwalk view to the TreeHouses, they would be our favorite.
We also recently got the last tree house when booking at the 11 month mark for January 2011. Do you have enough points that you can book the entire trip and have your sister transfer you some OKW points? Or have your sister book OKW for the other half of the trip at her 11 month window so you at least have a place to stay. Then she can try to get THV at the 7 month window. I just get kind of nervous of being without a bed.
Either way good luck. We loved the Tree Houses....