The sentence is ambiguous - it's unclear who was late based on the grammar alone.

"She" could refer to either:
- The nurse (meaning the doctor called the nurse because the nurse was late)
- The doctor (meaning the doctor called the nurse because the doctor herself was late)

Without additional context, both interpretations are grammatically valid. In real-world usage, we might lean toward thinking the nurse was late (since calling someone who is late is a common scenario), but the sentence structure doesn't definitively tell us.
