When you (or the song writer) was younger, they were small, quiet and shy. They didn't speak much, and basically let people get them down. But, as she grew up she learned what to do in these situations, and because of what they said, so she thought she was not pretty, and such. So "I'd tell her to speak up, tell her to shout out, Talk a bit louder, be a bit prouder, Tell her she's beautiful, wonderful, everything she doesn't see" telling her younger self to believe in herself, but sadly she can't do that, because that was the past uvu.