Well you could take her to your LFS and ask her what looks appealing and then come home and show her how to research the fish and how appropriate it may be. Never any harm showing a child the importance of buying fish responsibly.
she has been doing this with me from the start, she and her bro(6yr old) never cease to amaze me with what they pick up from trips to lfs/listening to me and mum talking. i brought a pair of oscars home last week and they were panicking in case i put them in with the small fish 'they'll eat them dad you cant do that'