Her voice is lower than a mezzo. Would that be a contralto? Or is the classification inappropriate at all, considering she was not a classical singer?
I would say she is a contralto or lyric alto. It is not inappropriate to classify singers like that even though they do not sing classical music. My voice teacher has a lot of pop singers who are lyric altos according to her. She also says that a lyric alto is generally not a recognized voice type but she has a lot of students whose voice type is exactly that.