There are 3 possible levels of response which vary in the amount of expense you need to incur
The first would be to sue in libel. This is notoriously expensive and uncertain as you have to show that what she has written is not only untrue but has damaged your reputation. This is why libel is known as the famous person's law because it means a public as opposed to private reputation and for that you need to be reasonably well known by the public at large.
The second option is to threaten libel proceedings unless you get a written retraction/ apology.
This may a certain amount of expense as it might require lawyers letters to try to achieve it.
The last course is to contact a newspaper and get them to write a story about how she has libelled you which has a nice poetic justice to it , it very cheap and may even involve you being paid for the story.
As a piece of litigation I would not recommend it, where to pitch the damages is the initial problem along with the other factors I have already raised.
I really did save the best for last