mycalmX what is a tomboy? When you say your daughter is becoming one - what characteristics is she displaying that makes her a "tomboy" ie a girl who "acts like a boy".
Because - the moment you lost those characteristics (the ones you think make her a tomboy) you've admitted that those charecteristics are for boys. Therefore if a girl choose to display these - she is a tomboy.
And you've also accepted that there are certain things that are appropriate for girls (so your daughter that likes pink is not a tomboy because she acts like a girl - is likes pink frilly things) and the one who doesn't is a tomboy.
In that very statement you have ascribed one kind of behaviour as girlish and another kind as boyish. The girl who does/prefers this another kind is therefore a "tomboy".
If you don't see how gender is constantly produced - through language, rhetoric, norms, mores, discourse, images, merchandise, text and the world at large - this production often subtle and done over generations - then you're ignoring very many decades of scholarship and evidence on how gender socialisation happens and works within patriarchy.