Am I the only idiot that thought that title was rather suggestive? 
How would you handle someone trying to shaft you like this?
All I can say is that she’s either got no understanding that the contract was to pay for a certain amount of writing, in which case she’s stupid, or she’s a total bitch (several other swearwords omitted. If you’d like to hear them, our contract stipulates an additional fee.) who’s trying a rather lame attempt to cheat you, with the unfortunate fact that lawyers are tremendously expensive and it can cost you more than you’d recover to do it.
Don’t ever work for her again. And hell, if you can legally do this and know other folks in the area who are in the same line of work, warn 'em so she has a tougher life in the future.
In the 21st Century, we all use .pdfs. If one so chose, they could lock the documents to printing and copying which would be much better IMO.
Also, I believe that emails are as leagally binding as anything else, so sticking to those will probably a) encourage her to be more open than she might if you got into sending certified letters back and forth b) save you some postage. Just be sure to keep the emails (and your sent folder).