hi
may i ask how old are you?
well hun its her problem not urs maybe she had some bad experience before. so she do not want to relive the pain. if you like her you can be a friend to her, in this case both of you win. with time she can trust you more. and who knows your relationship might develop. meanwhile try to find some one els after telling her of course that you becoming just friends means you can both see other people. if she does not like you you cant force her too. but with time she will know how much you care for her be open and tell her whats in your heart.