@kuustarr : If you are looking at a PhD, not just a masters. A) It is usually not good to complete it at the institution you did undergrad. and B) Maybe considering double majoring in human health with something like Environmental Science which, perhaps to your surprise has many more DIRECT links to programs in the Rollins School of Public Health including two Masters programs (I think 5 year or 4 year so not terminal) that may provide better preparation for a PhD at another school awesome in the area if that is what you are thinking.
You could get into NU (don’t say you won’t get in. That is ridiculous. You certainly have a shot. Believe it or not, as selective as NU is, it isn’t Harvard. You don’t need to be perfect to gain admission unless you are maybe pre-engineering or something. You just need to be really good which it appears you are), but for UG access to non-premed health related curricula, I think Emory is better 
. Though I am sure many are just more into NU’s higher USNWR rank.
Your chances are better at Oxford primarily because you have a super strong GPA (Oxford accepts a wider range of GPAs than main, while scores of admitted and enrolled students are virtually identical), but your SAT for Emory vs. Oxford is a wash essentially. Also, I hope you get into main because it is a better place to start if, again, you are non-premed but into healthcare (specifically public health). You get instant access to such courses whereas Oxford doesn’t really have equivalent Human Health courses nor courses in their Environmental Sciences (or is it Geology) that can easily be related to sustainability and health like Emory main. Oxford seems to excel more so at traditional environmental science and geosciences.
Either way, I think you may be a match, but keep in mind, it is RD, so application volume is heavy and there will be a lot of randomness. It could possibly end up that Emory denies or waitlists and that you make the cut for NU. You really never know. When in doubt, assume you are reaching a little for any top research university even when your stats or profile say that you are a match.
Also, those dual enrollment credits. Can you list some of the courses? I just want to see if there is any direction in them that could be sold as I don’t know what an “elective” is. “Elective” college courses for a high school student? Are these like a smattering of random intro. courses (basically you taking a bunch to enhance your course rigor index) or did you select them seriously based on key interests?