Do you mean Barbara Streisand? Just a studio singer? Have you ever seen "Hello Dolly"? Funny Girl?
Actually I haven't but you make my point. Movies are studio productions, not live events.
Barbra is not big on live performances and she made her mark and sold recrods and CDs based on her voice, not her stage presence and personality. Her movies were not what sold her songs. She was, IMHO, the greatest female vocalist of her time which lasted until Celine and Whitney came along. She had a great run.