Great idea about the clear dog thingy Gary! If you can't get one, you could always just make the 'hoop' frame and windshield frame, and tack/glue in thin plastic or thick polythene, the type you might find at a 'Garden Centre', used for greenhouse sheeting or covering plant thingies. The 'hoop could be cut MDF, or sections of bent ply or even the coffee tins again, and the front frame just strips of ply or similar. If you do use the tins though, make sure they are either covered in filler, or easier and stronger, wrapped in Duck tape or similar, then painted, so that Jemma won't cut herself on it.
Just thought - you could adapt a plastic/fibre glass or aluminium bicycle mudguard for the 'hoop' !