Mailing her an invoice is the way to go, make sure you have a copy too of course. There is no reason for her to not pay you for the work you've done and if she doesn't like it she can call another tech and see if she gets any better of a reception lol.

I've run into clients who can't seem to get ANY tech to even look at their computer because of them having a history of not paying techs and generally making their lives miserable.