Why did Taylor insist that Turtle reserve the name “Ma” just for her?

Turtle and Taylor wait in Oklahoma City for the adoption paperwork to clear. Turtle plays with Esperanza's medallion of St. Christopher. Taylor tells Turtle that she counts as a refugee, for she is as "tempest-tossed" as they come. Taylor had remembered "tempest-tossed" from the inscription on the Statue of Liberty. Taylor tells Turtle that she has only one Ma now. The rest: Lou Ann and Edna and Mattie are all friends, but Taylor is her Ma.