Step 1: Understanding the situation.
The nurse in the hospital could claim that the little girl is her daughter because the nurse might be the girl's mother’s sister or the girl might be adopted by the nurse, or there could be another situation where the girl refers to the nurse as her mother due to a close relationship.
Step 2: Conclusion.
The most plausible solution could be that the nurse is the girl’s aunt or a close family member, and the girl referred to her as her mother.