One-woman means one woman does the whole thing by herself. She performs it, runs it, or controls it — there is no second person in that seat. A one-woman show is a play or a night of songs with only her on the stage. A one-woman business is one she operates alone. It is built exactly like one-man. Though actually, English still leans on the old set phrases (one-man show, one-man band), and one-woman is the matching form you use when the person is a woman. Many people now say one-person when they do not need to mark man or woman. One-woman can sound like a fact, or like a quiet bit of praise: look, she did this alone. It is ordinary English, not slang, not stiff.