The only logic I can see here is that she wanted to stay in the ACC which means Tennessee and USC are out, even if they seem like more obvious choices to go. If she wants ACC, her options to play on a very strong team include:
Louisville
Duke
Florida State
Notre Dame
North Carolina
Louisville is a bit far and they have Durr coming in who will most likely be a better player than Brown. Florida State will be very good next year but should drop off considerably in 2017 and 2018. Notre Dame is stacked per usual, but they are loaded with guards and it is far from home. UNC is going to be hit with sanctions that could be brutal, which leaves Duke. That said, what surprises me is that she chose Duke when Duke has so many good guards coming to Durham in the next few years, particularly Salvadores. If she is able to bring Duke back to the Final Four, it'll be a pretty impressive career for Brown even if she doesn't take home a title, considering she helped resurrect Maryland and would essentially be doing the same at Duke. She is also an outstanding student and will get a top rate education at Duke which could have factored into her decision making.