Probably because I have a son, 3 nephews, 2 daughters and 6 nieces, 7 half siblings, and 2 sisters and am a psychology student?
Oh I like that reply Serious,why didnt I think of it, seriously it could be a good idea!!!
Just leave her alone. She's a child and you can sometimes do more damage by forcing behaviors.
If you are really concerned and REALLY have to do something about it get some girly toys that YOU can use when playing with your daughter and then maybe she'll emulate you.
I was like that growning up..I'm 31 married to a man and still a tomboy. I can remembering wanting to be a boy sometimes because it seemed easier, wasn't expected to be all girlie. Give it time.
PS and if she is a gregarius child guys games are a lot more vigorous and fun, maybe its part of her outgoing Personality.
So she has an older brother she is emulating? I guess the Boy toys are his,well you probably have introduced a few girl toys and Babrbies but I dont think this is a problem in any way, dont make an issue of it and she may well start liking girl stuff aswell its fairly common especially as she sees her cool bros playing with them , I kind of like them aswell.