Guys, stop letting 'strong' confuse you. It's just put there to differentiate from the normalcy of poorly written female characters. A female character who is physically strong can be 'weak' if that's her only defining trait. Too often people confuse a masculine female with "strong" which is entirely counterproductive.
"I’m a female writer and, what’s interesting about the Wizarding World is, when you take physical strength out of the equation, a woman can fight just the same as a man can fight, a woman can do magic just as powerfully as a man can do magic and I consider that I’ve written a lot of well-rounded female characters in these books." - JK Rowling