From my point of view as a parent of a girl, the ideal would be for my daughter to join a well-established, long-running, girls-only troop which has long experience using the BSA program. Unfortunately such troops do not exist now, and will not exist in 2019, though they might possibly exist in ten years' time.
For I do see benefits to a single-sex enviroment, for both the boys and the girls, especially for the middle school grades, and especially for kids who attend coed schools. But a well-functioning coed group might be better than a poorly-functioning single-sex group.
So that