Sounds like there’s a psychological/ personality component to this story that we only partially understand. My guess from reading between the lines and sensing your indignation is, that you came on a bit strong about the proprietary nature of the work, without a strong legal grounding for the argument.
You caught her basically “cheating” on you, called her out in her own office, and no matter how nicely you may have put it, she took that badly, and lines were drawn. I think you’re done there as long as she’s in charge. I suppose you could try going over her head, but that’s only going to make her hate for you permanent.
If you were a cruel and vindictive person, I suppose you could send a CAD request to YouTube to pull the clips for violation of copyright. The way I understand how this goes, Youtube generally pulls the clips immediately upon the first formal request, just on anyone’s say-so, to be on the safe side, and then it’s up to the disputing parties to prove who owns what before the clip is allowed back on. Which may take a long time.
Generally this tactic happens when someone posts a clip from a broadcast TV show, music video, or commercial and the copyright owners complain. Should this happen to that fine company, and their web visitors go to see clips that are no longer there, that might be bad for business. If you were to employ this tactic, and I’m not suggesting you should, I bet you would be getting a call back from the lady or her boss right quick. To her boss you can explain that this all got out of hand because the lady didn’t understand how things are done, acted unethically, if legally, and you’d be happy to make things right again at little or no charge if the boss would let you. But it would be a Pyrrhic victory at best, I fear. Pyrrhic victories are too expensive for businessmen.
No, I think your best bet is what the guys above have already laid out for you. Consider it like a no-fault divorce, send her all the stuff they paid for, and forget about them. If they come crawling back for anything, bill them quite stiffly.
When the management reshuffles at that place, if you left everyone else there on good terms, you might get a callback.