When you're evaluating this role, it's not enough to just look at the high notes. You also have to look at the guttural low stuff, the speaking, and the screaming. Over the course of an evening, it's a lot to put a voice through, even a highly trained one, which is why Maria Callas, of all people, said to Andrews backstage that she couldn't understand how she could do it every night.
In addition to Andrews, Melissa Errico and Cheryl Kennedy also developed vocal issues in this role, with Kennedy, if I remember correctly, having to drop out of her Broadway revival right before opening night. Errico missed a large portion of her production's pre-Broadway tour. I think Martine McCutcheon also had problems in last big West End revival...I seem to remember hearing that she missed a lot of performances.