You seem not to be following this story (or the news).
Some performers have children too young for the vaccine. Osnes decision puts them at risk.
There are breakthrough viruses, so though her collegues are not likely to die, they can become ill. The effects of the breakthrough viruses can linger, so singers could find themselves unable to sing. (The virus affects the lungs.)
Osnes can certainly forgo the vaccine. She may have medical reasons not to. But if she does, it is not right for her to accept work that makes her a hazzard to others.