Myself and a few other family members attended Montessori.
I dont know your religious background...but that is one of the first things. Its more spiritual though
What they provide is a more interactive, creative and "every day" learning approach can be extremely beneficial.
While every school and instructor is obviously different overall I believe there curriculum allows for more THINKING and that is very important especially I think for young girls. It creates a lot of independence and confidence and usually you wont find that in more traditional settings. They create a voice early on, not afraid to ask questions and a great educational foundation (like developing memory and comprehension etc.)
Finally...it can be VERY expensive.
If it is accessible and possible I think its a great option but it is possible to create this environment at home with some work.