The flight attendant told Albuquerque International Sunport aviation police she removed the 13-month-old after she saw the mother slap the girl and passengers complained.
A Southwest official said the baby's parents were arguing on Flight 879 and the child was upset, so the flight attendant offered to hold the baby.
Airport spokesman Daniel Jiron said paramedics checked the baby when the flight landed.
Aviation police returned the child to her parents after speaking to the couple, the flight attendant and other witnesses. The parents were not cited.
Dallas-based Southwest Airlines said the couple was later cleared to take a later flight to their final destination.
Aviation police chief Marshall Katz said authorities felt it was an isolated incident. He said the attendant's decision to hold the child neutralized the situation.