ouch-tough one…clearly she did not uphold her end of the contract so by rights you don’t have to pay her anything. I would be clear that upon receipt of evidence (anything at this point) that she was in fact actually performing SEO on your site payment will be forwarded. Put a time to it-like 7 days whatever. If she doesn’t deliver I would walk. Not the kindest response but business isn’t built on kind-it’s built on trust, credibility, and performance. You can also use a tool like Mangools (free 10-day trial) that will tell you what and when backlinks have been added to your site. If you’re set up on GA you can view those reports too. But at the end of the day, you should know just based on the number of calls/clicks to your website if she was doing what she promised.