The second ray of the dorsal fine is usually elongated on males. Also females usually have blue speckles in the black spot on their side. Also i believe the pectoral fins dont extend past the anal fin on females. Males usually do extend past the anal fin.
I cant see the picture so i dont know. But it might just not have a pink belly yet because of stress. Or maybe she's just to young to tell yet.
Anyway, i hope it works out for you ^^. Good luck.
Edit, i was just able to see the picture.
Congrats i'm pretty sure its a girl