best preschool curriculum for a highly sensitive child
The best course of action is to observe a class, perhaps more than once, before you enrol her. You'll need to find out if the atmosphere in the class suits her needs. Even if a particular method seems like it would be a good fit, you won't know whether the implementation actually works for her.
My dc attended Montessori. Their classrooms had a calm, gentle, focused energy despite having fairly large class sizes for pre-school. There was about 20 students and 2 teachers. The students were encouraged to regulate themselves. When the noise became too loud during the 2 hour work periods, a student would ring a bell to get everyone's attention and suggest that they work more quietly to prevent distracting each other. However, reading and hearing about other experiences in different Montessori schools, I know that other schools don't promote this kind of classroom environment. The only way to know whether a class will suit your child is to visit, observe closely and ask lots of questions.
Good luck with your search.