How had Maria become the chief director of the Legend of Anne?

Even though she was only the acting chief director, it was still an incredible feat.

What qualifications or skills did she have to achieve it?

As if reading Bill's mind, Vivian said sourly, “As the script supervisor, Maria was with Mr. Jackson all the time. Out of all the crew members, she knows best about his vision for the show. Therefore, after Mr. Jackson fell sick, he directly appointed Maria to take over his position as chief director. Of course, she is just his mouthpiece."

Hearing this, Bill understood how Maria had clinched the position of chief director, but he thought it was a pity.