a closeup of Shelley from her Breck ad, 1972
Shelley endorsed many products in 1970s and one of them was Breck. Yes, she was a Breck Girl as well - like Jaclyn Smith, Cybill Shepherd, Kim Basinger and Cheyl Tiegs. She endorsed the variant Breck Basic Texturizer which was formulated for thin, fine or limp hair to give it "crisp body that hold so beautifully". Shelley even appeared in a Breck commercial herself. Check it out at:
Texturizing Shampoo
Shelley in a 1972 ad for Breck hair products