I found this in Facebook help… I don’t think you can set up a ban for just anyone; they have to have Liked the page (you can check if this user has liked your page; he would have to do so in order to post on the page).  You may just have to wait until the user decides to post on the other pages to put the ban in place. Hope that helps.

How do I permanently ban someone from my Page?Basics » Explore Popular Features » Facebook PagesExpand All · ShareHow do I permanently ban someone from my Page?From your Page:

1. Click the like this link or Insights tab in the left-hand column.
2. Click See Likes in the top-right corner. For Pages with the new timeline design, open your admin panel and click See All in the New Likes section.
3. Select the X next to the name of the person you wish to ban.
4. Check the Ban Permanently box.
5. Click Okay.

1. Click  next to a post by the person you wish to ban
2. Click Delete Post…
3. Select Delete and Ban User

1. Click the X next to a comment by the person you wish to ban
2. Select Delete Comment…
3. Choose Delete and Ban User

Thanks, @fayebrogi and  @russellallert ~ I thought that was the case because I’d combed through everything and couldn’t find a way to do it.  Guess I’ll just have to see if she posts on the other two pages.  Crazy when you get told to ban one of three owners because she’s a troublemaker!

You can pre-emptively ban someone @dedimason – just follow the tips in the first section of the Help.  You have to comb through all the Likes to find them first but then you can ban them before they post.  

Yes, doesn’t sound like a good relationship!  :)

That is crazy. 
I think you can report her by page/name/comment etc and even ban / block her if necessary. Change passwords etc.