Here is an estimated timing map for you. This is based on the 2018 marathon course, but they should be really close.
I chose two different possible marathon times based on you saying she has run a sub-90 min HM. This is a 3:07 and 3:19 marathon projection. This estimates she will be at TTC around 5:59-6:01 am, Poly around 6:25-6:28am, AK exit around 7:11-7:17am, DHS exit around 8:17-8:28am, Boardwalk around 8:25-8:36am, and Finish around 8:38-8:50am.
If you go to DHS or Boardwalk, you are unlikely to beat her to the finish line when factoring in you driving, parking, getting through security, and walking to the finish area. WWOS is possible, but if you go to AK, then you're unlikely to beat her to WWOS (unless you plan to see her exit, but then that's a crunch to the finish).
So possibly, TTC, then Poly, then WWOS, then Finish?
Given her expected finishing time around 3:08-3:19 there won't be many people finishing with her. In my experience the finish line is not crowded at all and you can very easily see your runner from the non-Chear squad grandstands. You've got about 4-10 people crossing the line per minute at that time in the race. I've finished in 3:15 and 3:20 and my wife has caught great pics of me crossing and we've chatted for a few moments in the finishing chute (while she stands in the spectating area).