Because she's a girl:
www.theguardian.com/sport/2017/oct/27/us-teenager-who-won-golf-competition-denied-trophy-because-she-is-a-girl
If she'd declared herself male I'm sure it would all have been fine and dandy. Or would it? I wonder how men would feel having their trophies taken by women. I suspect that they wouldn't take it lying down.