First, I think you should have been more clear of your intentions in the first place, like when you first started spending time together, but that is a moot point at this stage.
Second, I won't preach to you, but you may just have to give her some space for right now. Just be there, reminding her that you would really like to be a bit more serious with her, but if she is going to continue making very poor decisions (like that hooking up bit) are you sure you really want to be more serious with her? I know not all of us are perfect, but if she develops a history of this, it may not be the best idea to continue pursuing her. You might get hurt pretty badly yourself. I can say that because I have gone through something similar to this, and it turned out in that way. She repeated her behavior.
To put it simply, be there for her, but keep in mind that people rarely change. I apologize for being a bit of a raincloud, but someone has to say it, and I don't want people getting hurt who didn't earn it.
Second, I won't preach to you, but you may just have to give her some space for right now. Just be there, reminding her that you would really like to be a bit more serious with her, but if she is going to continue making very poor decisions (like that hooking up bit) are you sure you really want to be more serious with her? I know not all of us are perfect, but if she develops a history of this, it may not be the best idea to continue pursuing her. You might get hurt pretty badly yourself. I can say that because I have gone through something similar to this, and it turned out in that way. She repeated her behavior.
To put it simply, be there for her, but keep in mind that people rarely change. I apologize for being a bit of a raincloud, but someone has to say it, and I don't want people getting hurt who didn't earn it.