My dd7 would use pronouns only if she could. But I always tell her - give more details, who is "they", there are many characters in the story, you need to be specific.
This was a while back.
Now I just say "no pronouns, please". And she corrects herself.
Yes, that is a complete sentence, using the pronouns, but it is not a clear sentence, or with enough detail. As soon as the story is slightly more complicated, then he, she, they become very confusing.