Betty is a mermaid in a movie named Mermaids. Betty was portrayed by two actresses: Geneviève Lemon (older) and Holly Brisley (younger).
Betty is Earl's wife, and she has forgotten her mermaid heritage after spending so much time on land. Venus gives the birthright shell back to Betty, causing her to transform back into her younger mermaid form, and urges her to return to the sea. Betty, however, declines, because she now has a human daughter, Tessa, and instead asks Venus to keep her birthright safe.