Hmmmm well you hit the nail on the head. You have to lay down the law =( I'm so sorry this is happening. But it is your money, your time, and you're hiring her to help. So you do have to get direct. I would bring it up first thing when you next see her. Tell her again (and again if you must) that you think she is only looking at the past, and that you NEED her to look at the present without the past influencing it. And, really, if she can't do that, then she's not the right person for you to hire.
I do hope this works out!