“She is totally committed to the material, whatever it is,” he said. “Things can be raw, they can be intense, they can be funny. But she’s always in it, totally. Obviously over the years, her voice has changed, but the commitment has not gone anywhere.”

Similar appraisals come from other colleagues. Ivo van Hove, the “Mahagonny” director, said that she is “a personality, of course,” but added that she is collaborative and takes her job very seriously. And Peter Gelb, the Met’s general manager, described her as “incredibly brave,” willing to bare herself both emotionally and, in the case of “Salome,” literally.

“She has the courage and the acting skills,” Mr. Gelb added, “and she’s able to do this without compromising her marvelous technique.”

Even so, because of Ms. Mattila’s changing repertoire and busy schedule, it can be a challenge to find roles for her at the Met. But, Mr. Gelb said, “she’s one of the great singers and dramatic presences that’s ever been on the Met stage, so I will make it my business to do so.”

As she approaches her 60s, Ms. Mattila has her eye on Wagner, a composer she has long resisted. In the past, she said, she couldn’t bear the thought of sitting through five hours of “Götterdämmerung.” And once, while reading the score of “Tristan und Isolde,” she got halfway through before thinking, “Doesn’t Isolde ever shut up?”

But last year, she sang Sieglinde in Francesca Zambello’s production of “Die Walküre” at San Francisco Opera. And, for the first time, she watched the rest of the “Ring,” as well — which meant sitting through “Götterdämmerung,” and, she said, “crying for five hours.”