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.

From the waist up, Milagros seems normal, smiling and babbling like any baby. Below the waist, her abdomen flows seamlessly into her legs, which move separately but are trapped in a “sack” of tissue and fat down to her heels. Her tiny feet are splayed in a “V,” completing the look of a mermaid’s tail.

Milagros’ rudimentary anus, urethra and genitalia are all located together but genital reconstruction will probably wait until adolescence.

Rubio, who has been caring for Milagros since she was two days old, said she would have several more 30-minute high-pressure oxygen treatments in a hyperbaric chamber to increase oxygen flow to the skin.

Hyperbaric chambers are used by scuba divers to treat decompression sickness, or “the bends.”

Milagros’ condition forced her parents to leave their home in the Andean town of Huancayo and move to Lima, where they live largely on charity. She has been treated for free by a City Hall-funded hospital run out of old buses.

Her father, Ricardo Cerron, 24, got some work as an electrician at the hospital, but the couple worry about making ends meet. Her mother, Sara Arauco, 19, dreams of “having something so she can be happy, a little house” for the two decades of grueling operations facing Milagros.

Milagros will be baptized in Lima’s cathedral on Feb. 21. Lima Mayor Luis Castaneda will be her godfather.