Fish - boy or girl platy????!!!!!?

I have 1 female platy and ever since i got other female platy's her anhal fin now looks like a boys. ';It'; try's to mate with the other females. ';it'; never puts it back like girls. And yes i no how to tell if it is a girl or a boy and no i am not getting confused I am 100% sure. But can they change genders??

thanxFish - boy or girl platy????!!!!!?
no, they can't. you probably mistaked it for a female when you bought it. males have an anal fin like a stick (gonopodium). female's looks more like a triangle.

http://farm1.static.flickr.com/212/46584

above is a female

below is a male

http://fish.orbust.net/images/male2.jpg