Final answer:
In the sentence, 'she' refers to Jen, who is the subject cheering and feeling proud in the given context.
Step-by-step explanation:
In the context of the sentence 'Jen cheered loudly; she was so proud', the pronoun 'she' refers to Jen. This is clear due to the structure of the sentence, where Jen is the subject performing the action of cheering. Therefore, when we refer back to the subject with a pronoun, it's understood that 'she' is referencing Jen who is expressing pride, likely in Renee's performance.