There is no way to block a follower, but there IS a way to get rid of plagiarists. If they're hosted at Wp.com it's fast and easy: go to their site and on the grey Admin bar you'll see the blog name. There's a drop-down menu to Report as Spam. Report her, giving the URL of your writing and the URL of her plagiarized writing, and staff will deal with it. They routinely suspend entire blogs for this sort of thing. YOu may also have to file a DMCA, which is no big deal. http://labnol.blogspot.ca/2007/09/dmca-notice-of-copyright-infringement.html
If it's not hosted at WP.com, find out who does host it and send that to them.