Thanks for the questions NSG (hope abbreviation ok!). We will be in DC.
I have looked at the SATs which she can sit here and am contemplating having her sit before they change to see how she goes. American University doesn't require SATs but most others I have looked at will.
She finishes school here in Nov/Dec 2016. I am not sure she will have her results in time to apply for the Spring 2017 intake so likely looking at Fall 2017. The way our school years are offset makes it difficult. Gives us a little more time.
We will be renting and we have some choice but have to be inside the Beltway.
I will start a new thread shortly.
I probably should wait till you start a new thread. But a few comments on your situation. My DS should be graduating H.S. June 2017, so would be also applying to schools about the same time. As to applying for a "spring" Jan 2017 admit. Check with the schools to see if they accept spring applications not all do. It might be more comfortable for her to wait for 6 months but you might not be able to wait till you move to start the application process.
Keep in mind for a fall 2017 admission she many have to apply before you move. Application deadlines vary but are often due the fall the previous year, so be sure to check at each individual school. This is well before you even finish first semester of senior year. And in those situations she might not hear until they get in until March. In addition many private schools applications want teacher recommendation letters and detailed letters from the school that probably are easiest to get before you move.