I was going to say that the chance of admission to “Rosemary” is precisely zero since it does not exist as such 
OP: please heed the advice here. Think about why you want to attend BS. Why the schools you listed. What’s Plan B if you don’t get into any of these (i.e. good local public option? local day school?) Etc.
In almost all certainty, there are many other schools where you’ll fit, be challenged, and thrive. If you want to “go to BS” then please add schools with meaningfully higher acceptance rates. Check the various Hidden Gems threads.
If it’s ACHE (my new acronym for the four schools you list) or bust, please keep in mind that these schools reject 85-90% of applicants, many of whom are highly qualified, with SSATs into the 9x percentiles, 4.0 GPAs, tons of ECs, and yes, taking many subjects years above grade-level, etc.
I say that not to discourage you believe it or not! But rather to encourage you to reflect on the questions I and others have posed. Get to know the schools in question…how are they alike? Different? What attracts you to them independent of the name on the sweatshirt?
Try your best to demonstrate that you’ll be an interesting, interested member of the community at school X. Be specific. Your reasoning for X won’t necessarily be the same as it would be for Y.
Good luck - we’re happy to help. Tell us more…