We only looked at mid-Atlantic schools for our DD and a strong theatre program was one of her top priorities.
Of the three schools that we focused on (Mburg, Peddie and Blair), I agree that Mburg might be the best fit for her. The theatre program had some very cool classes (stage combat!) and chose productions that were quirky and a little outside the box. It also has an outdoor education program with a variety of activities from rock climbing to kayaking and hiking.
I’ll put in a cautious plug for both Blair and Peddie, at least to look into. Peddie has great theatre (I’ve talked about some details in other posts) and an academic support center which my DD has taken advantage of for extra math and writing help but I can’t speak to any specific ADHD support. I’m not aware of significant outdoor activity options other than the annual sophomore bike trip.
I was very impressed with Blair’s curriculum for 9th graders which they call “Habits of Mind” and teaches research based strategies for time management, learning retention, and study skills as well as general health and wellness. They also had the most robust approach (IMO) to “scaffolding” for the students as they progress each year towards graduation. I don’t know about any specific outdoor program at Blair. The theatre program seemed strong (but not as strong as at Peddie).
Love the idea of Proctor (the off campus experiences look phenomenal, I wish I could go back in time and do them all!) and Millbrook too. I suspect your DD will need to prioritize what is most important for her (theatre? outdoor experiences? location?) and match it to the schools that offer her the learning support she needs.
Good Luck!