Hi Jacob,
First a question, are you coming for 4 months from Jan - Apr, or for a shorter time in that period?
I don't know how familiar you are with Maui so pardon me if I am giving you some obvious generalities first. Maui is called the valley isle because it has 2 volcanos connected by a valley which is where the main city, Kahului, and the airport is. It is not where I think anyone would want to stay for any reason unless you want to live next door to the Walmart.
The West shore of the south half of the island is the main tourist area (Kihei). It is on the dry leeward side of the island and might be where your sis would prefer to stay with it's famous beaches and miles of condos. Most condos are rented out through agencies and I know a few. There are also some rented out privately and we had a list at one time but i don't know how current it is. On rare South (Kona) or North wind days you can sail the relatively flat water there. It is not my preference and we go longboarding rather than sail there. It is about a 30 minute easy drive to the "best" North Shore windsurfing areas that stretch from Kanaha (almost under the airport) to Jeff's house, camp one, Spreckelsville, Baby beach, and then continuing on the east side of Paia, blue tile, lanes, Hookipa and Jaws. There are beaches here that my wife and I find very beautiful, but keep in mind for the non windsurfer, that they are on the prevailing wind side of the island. There is accomodation along here that is I think is Giampaolo's specialty.
If you go South from the North shore up the volcano (upcountry) you get away from the tourists into the higher, cooler, wetter, quieter, less expensive, more remote areas such as Haiku, Pukalani, and Kula. This is where we stay and I can give you a some good recommendations. We find it ideal to just crash after an exhausting day on the water in the rainforest, just be aware that this is not the Hawaii of the postcards and it may not be your sis's choice.
For completeness sake i will add that there is a large area on the West side of the Northern Volcano end of the island (Lahaina area) In my very biased opinion it is very expensive, hot, remote and for those who want and can afford an airconditioned luxury hotel and want to sip funny named drinks with an umbrella at the pool.
If you can give me a bit more information on what you would like I would be happy to continue. If you would prefer to keep the specifics confidential feel free to e-mail me. If you think that it would be of general interest just continue here.
Aloha,
PS, GP please correct any errors that I may have made.
Dolf (83kg, 183cm), Joanna 24% less weight and shorter.
SOS Big Red; RealWind 270XL; Thommen custom 105 , MWX 92, 83, 74, custom 67 ; JP Rad Wave 64
UL Freaks: 9.0, 8.0, 7.0, 6.3, 5.8, 5.3, 4.7, 4.2, 3.7, 3.2
For Sale: RealWind 270; Starboard E80, E70, E62