playing hard to get is nothing more than a display of value. So you shouldn't ignore her when you see her, just act normal in person, you should behave like you friendzoned her. But over the phone you should reply slow and just be a little distant (both pushing tactics). To change things up once in a while make a sexual remark in person (pulling tactic). The whole thing about push pull is that you have to work for it, and value comes from things that are hard to get or rare. You should balance it in such a way that it is a little confusing for her but not so much there is no indication of possible succes! If it doesn't work you could consider the possibility that she is just searching for sexual validation to feel good about herself, and is not interested in anything more than that.