It is still worth a try but in looking at your photo, I don't think gluing alone is going to work. You could attempt to Weld it (after the superglue has set) with a pencil type soldering iron. That is if you have one. Take the shoe off of the flash and draw the iron tip across the joint on each side of the repair. Just enough so it melts the plastic together. Take care not to inhale (or let your daughter inhale) the fumes. You may have to take an emery board (fingernail file) or a needle file and clean it up afterwords.
Really though I would just contact Metz and get another shoe.