Should I be further denormalizing?

Question

I'm working on a messaging app. I want to be able to display the senders username. I'm currently modeling messages and users and trying to display username by query the usersRef by the authData.uid.

Messages { 
  sender: authData.uid,
  body: decoded,
  created_at: Firebase.ServerValue.TIMESTAMP
  }

Users {
  email: user.email,
  username: user.username,
  created_at: Firebase.ServerValue.TIMESTAMP
}
// This returns https://talklah.firebaseio.com/users/simplelogin%3A3/email
$scope.getUsername = function(sender) {
  var usersRef = ref.child("users");
  return usersRef.child(sender).child('email');
}

// I want to display something like this in my templates
message: Hey, how are you? (sent by [username])

How should I be approaching a problem like this?