I would keep it between you and the dental assistant unless it becomes a recurrent problem. If you explained to her the reason and she understands not to sterilize it then there is no need to take it any further. Some people don’t know until someone tells them otherwise. Sounds like she didn’t know any better and made a mistake that hopefully she won’t do again.
I agree with WarnerSL. If you would like to show her a link to a study for educational purposes of why not to sterilize teeth with amalgam here is a link: http://www.ncbi.nlm.nih.gov/pubmed/8636514
Thanks ladies, that is ultimately what I decided to do. I was just worried that it should have been documented and didn’t know if either of us were at risk for handling it. Thanks for the link