Ok this is just a theory and you can agree/disagree all you want. I haven't looked at any spoilers so this is just a hunch.

I think Dan somehow hired Nanny Carrie to try and break up Naley and kidnap Jamie. Here are my reasons:

1)He knows IF he ever gets out he will never get to see his grandkid. Nathan and Haley have made that perfectly clear.

2)He has those connections and money which Carrie needs for grad school

3)He's done it before (remember Jules?)

4)He got Carrie to get Jamie to trust her so that when he gets out he will be able to see him because he will go with Carrie if she takes him.

Just a theory but who knows she could just be a psycho but her arrival just seemed TOO perfect just like Jules.