The Amazing Mrs. Holliday (1943) is one of Ms. Durbin's more dramatic films. Durbin plays a missionary who aids orphans in war-torn areas.
Tom at The Amazing Deanna Durbin Blog has written a review of that film here: The Amazing Mrs. Holliday (1943).
Tom makes an excellent point that the movie is so realistic that for awhile "it almost felt like an autobiographical film." He's right - the first half of the film is like an engrossing documentary or newsreel. The studio-controlled star was rarely allowed to do straight drama, which is one more reason to see this movie and enjoy a not-as-well-known side of Deanna Durbin.