Postdoc that refuses to follow the terms of her contract
Your additional information that you put under the comment section and I think it should be placed in Question also, is that post-doc is paid for by the University, not paid by you/from your grant. So you are not PR, you are an advisor.
Nick S, pointed out something that is not specific for mathematics, also physics, material science, applied science, engineering and some types of medicine (biomedicine), I will quote him


  a Postdoc position is supposed to be the time when the researcher
  starts working independently. I don't know how it is in your field,
  but for me a postdoc wanting to work independently would be a good
  postdoc.


Dan Fox also pointed out very common thing 


  A postdoctoral supervisor's primary responsibility is to help the postdoc develop into an independent researcher, if the postdoc is not already an independent researcher. The notion that a postdoc should just take orders and be another cog in a big machine is sad. So is the notion that a postdoc who independently obtains interesting results should add the nomical supervisor as a coauthor.


At my university, it is explicitly written in contract that mentor/advisor needs to be the corresponding author of a paper from a postdoc.
I am aware that some contracts don't have this clause, and they can be purely independent.
However, if this is the case with her contract, you should stop giving her any resources. If she is not dependable on your resources and still yields some kind of results that are publishable, I am sorry to tell you this, but according to info that you provided in your question, she is in the right.

You need to report progress as it is to head and to above you body.
You need to be honest with people that are above you that you don't have any control over her and that you don't know direction of her investigation. Does she know you need to write a report about her progress? I think if she knew that she was evaluated, she would tell you how far in research and what she is doing now.
Again you should be more precise about the content of her contract.
As far as I know, contracts with universities are very liberal and give a lot of freedom to the postdoc.