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."
In this sentence, it's unclear whether "she" refers to Cindy or Patricia. To improve clarity, you could replace "she" with the name of the person who noticed the sign. For example:
"While Cindy and Patricia were walking down the hall, Cindy noticed a sign on the teacher’s door."