Which sentence should be edited for pronoun clarity?

On the way to the post office with Donald, Gerald realized that he forgot to check his email.

The librarians received the box of new books, and they immediately opened and unpacked it.

The teacher told the class that she wanted their papers to be turned in by the end of the day on Friday.

While Cindy and Patricia were walking down the hall, she noticed a sign on the teacher’s door.

While Cindy and Patricia were walking down the hall, Patricia noticed a sign on the teacher’s door.

The sentence "While Cindy and Patricia were walking down the hall, she noticed a sign on the teacher’s door" should be edited for pronoun clarity.