إِذَا رَجَّعَتْ فِي صَوْتِهَا خِلْتَ صَوْتَهَا
تَجَاوُبَ أَظْآرٍ عَلَى رُبْعٍ رَدِي
Meaning: When she varies and repeats her song, you may think her voice resembles the answering cries of nursing she-camels over a dead young calf.
Rajjaʿat fī ṣawtihā describes vocal modulation and repetition. Aẓʾār refers to nursing or foster-mother she-camels; rubʿ radī evokes a young camel that has died. The simile concerns the responsive, plaintive quality of the voices, not a claim that a singing woman literally becomes an animal.