The sentence that should be edited for pronoun clarity is:
"While Cindy and Patricia were walking down the hall, she noticed a sign on the teacher’s door."
This sentence is unclear because "she" could refer to either Cindy or Patricia. For clarity, it should specify which one noticed the sign. For example, it could be revised to:
"While Cindy and Patricia were walking down the hall, Cindy noticed a sign on the teacher’s door."