A Peruvian baby dubbed the "Little Mermaid" because of a rare birth defect in which her legs are fused, is making good progress after initial surgery to prepare her legs for separation, her doctor said on Monday. "She's doing great, she's brilliant," Luis Rubio told Reuters after 9-month-old Milagros Cerron began oxygen therapy on Sunday to help her wounds heal. Doctors have inserted three silicone bags between her legs to stretch the skin to prepare for the first of two operations next month to surgically separate them -- one of only a handful of times the risky procedure has been attempted. Milagros -- whose name means "miracles" in Spanish -- was born with "mermaid syndrome," or sirenomelia, a condition that is about as rare as conjoined twins but nearly always fatal. Sixteen-year-old American Tiffany Yorks, whose legs were parted when she was a baby, says she believes she is the world's only surviving mermaid. Most babies with the syndrome die within hours. --More 2241 Local Time 1941 GMT