Have you given her the impression that you would not accept her, if she were gay?
This could be a passing thing, but my first crush on a woman was at the age of five and I did not really accept that about myself until I was 22 years old.  My mother didn't make bold statements against lesbians, but she made it clear with little statements and actions and with her desire NOT to talk about that.
I'm sure you are a very good mother, but, if she is worried that you find the discussion too uncomfortable, that might hinder her openness with you.
A book that helped me was "Annie On My Mind".  Giving it to her as a gift and also reading it yourself, letting her know that you are able to discuss it with her as she reads or finishes it, could at least open up the opportunity.
I am only going from my experience growing up.  I am sure this is very difficult, as a parent.  I wish you luck, love and strength.

Thankyou for your answer, it had crossed my mind that she might think or even be gay (how do I tell ? she likes boys and has had a boyfriend although I say that loosely as at 12 I think its more 'friend')and I have never given any negative comments to gay people I have always told both my girls whatever they are I would always love and support them. Neither myself or their father has a problem with gay people .. I will look into getting the book you recomended though, as it may help her figure stuff out !!.

maybe point out some guys to her that she might like if your comfortable with her dating.i thot thst i might like girls and then i  got a crush on a girl im in 6th grade its tottally normal once she gets a crush on a boy(or a girl) you and her will figure it out

Don't worry, it's pretty common for kids/teenagers to go through that stage of crushing on the same sex. I, myself have had a crush on my female teacher but I'm completely over it and I'm in a relationship with a guy. So it may just be out of curousity or she maybe gay. Just let her know your there for her but don't be to pushy, kids hate that.