Welll as an executive producer (not just a "credited' producer, y'all) who is on the show, she can actually call a meeting and fire a director. Shonda Rhimes and possibly Krista Vernoff (Showrunner) would probably have to agree. but yeah, she could do it. It IS in part her show. Should she? No, big no. I get why both got testy but no, neither have time for this and he was the director. As an actress she needed to find a way to work with him while supporting his power. As an exec, she had input before filming began and she could pull someone in an emergency but it would cost millions. Having the power doesn't mean you should use it. https://www.hollywoodreporter.com/tv/tv-news/greys-anatomy-renewed-ellen-pompeo-returns-season-18-4152478/