Mistral's poem "Fear" expresses a mother's anxiety that someone or something will take her daughter away, making her into something beyond her mother's child. Mistral's fear is that when her daughter would become a "swallow," "princess," or "queen," she would cease to exist as the speaker's "little girl."
Mistral's examples are from different ends of the spectrum, the first being a sparrow and the last a queen. The range of images shows the reader that anything her daughter could become would essentially take her away from the mother; she would be something else, something beyond just a daughter, and this results in the mother's loss. The speaker worries that if her daughter were made into a swallow, she would no longer "fly into my straw bed" or allow the mother to "comb her hair."
It is not unusual that a mother would not want her daughter transformed into a swallow, but Mistral emphasizes the mother's connection to her daughter and the anticipated depth of her loss of her daughter by also saying that she doesn't want her daughter to be a princess or a queen. Mistral seems to reference fairy tales here, and in most cases, a humble young woman's rise to a regal position is celebrated by those around her. In the poem, however, the speaker fears she would be irrevocably separated from her daughter if her daughter were elevated to one of these positions (the mother, it is implied in stanza one, is poor). The speaker worries that if her daughter were made a princess or queen, she could never rock her to sleep again.
In worrying about losing her daughter, the speaker also imagines a mysterious "they" who would take the daughter from her. This creates a feeling of competition between the speaker and "them." Even though "they" would "put her on a throne," the mother worries that "they" could not protect or care for her daughter the way she would. She clearly sees "them" as an enemy.
Using references to fairy tales and a range of images, the speaker effectively expresses the mother's anxiety about losing her daughter.