Well, there is a reason for it. Have you been loving her likes she wants to be loved?? You want her to put out? Make her feel cherished, loved, and even sexy. Be romantic without the expectation of sex. Start holding her hand, giving her small kisses, hugging her, putting your arm around her when you are out or just sitting on the couch.
Once she warms up to your little displays of affection she will be more apt to "put out".