Hi Simon, welcome to the glass message board.
This is a question which I'm sure you get a lot of answers to - but maybe it would be better to give her the keys to the pumpkin instead.
"Glass" in glass slipper is a faulty translation from the French "vair" which means squirrel fur, so not "verre" which is glass. I'd be highly suspicious of wearable ones.
If you look on google image (as I'm sure you did) you will find many fancy miniatures. The closest thing I could see was a 6" plexiglass one on Etsy, used as cake decoration or childrens parties. It would set you back 5 pounds or so affordable for a joke and disposable.
Good luck.