Isn't "Qui est-ce" an acceptable form as well?

Bonjour Susan, "Qui est-ce ?" is a closed question in itself, meaning "Who is it?", you cannot use it to ask "who is it [that....]". It's in that case that you'll use either "Qui [...]?" or "Qui est-ce qui [...]?". I hope that's helpful. À bientôt !

Merci!! Je comprends maintenant!