For the record, all names are ridiculous. The fact that a collection of characters (and sounds) is supposed to imply something about the person is odd. The only way we associate “boy names” with boy-ness is that we happen to know boys who have those names. Names are simply labels, and they are subject to trends and popular culture.
Harper happens to be a popular female name, and it’s gaining in popularity. In 2011, it was ranked #54 (can search here). At this rate, it could be at #27 once the 2012 numbers are released. Asking if “Harper is too tough and boyish” will likely sound like asking if “Sophie (ranked #1 in US) is too tough and boyish”.