The sentence is **grammatically ambiguous**, meaning it is impossible to determine with certainty who was late based on the structure alone.

*   **Interpretation 1:** If "she" refers to the **nurse**, the nurse was late, which is why the doctor had to call to check on her.
*   **Interpretation 2:** If "she" refers to the **doctor**, the doctor was late, perhaps calling to explain why she would not arrive on time.

Because "she" could grammatically point to either the doctor or the nurse, the sentence requires more context to be fully understood. In common conversation, people often assume it refers to the nurse, but that is based on social context rather than strict grammar.
