Depending how many there are, you can get a pretty frame, one with molded details on it is nice.(can even be recycled) paint it a color that suits the room it will be in using enamel paint for shine.
Remove the glass and pad the inside by gluing layers of quilt batting to the cardboard back that comes with the frame. Cover with a nice piece of fabric like velveteen, moire satin etc. and staple to the cardboard with small staples.Pin the pins on in a pattern that pleases you or the dancer who earned them.
Depending on her age, she might what to do all the crafting herself or help at least. Another way, is to make or buy a pillow and pin the pins to it. If the pillow had a pattern that is dance themed, that would be even better.
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