^ of course Ommmward's is the best approach....boredom is something very useful.
But you could try some of these, maybe:
Buy a desk or something from a charity shop and spend time stripping it and decorating it- or take some woodwork classes, which would be SO useful. Or decorate a guitar.
Go round skips in your neighbourhood and salvage things which you could glue up into a sculpture
Make a mini village from Fimo or clay
Have her take an electronics course so she can take apart a clock
Nat Geo collages
Make a doll's house- up to you how sophisticated it is
Get her into anatomy- she could make a really neat book of detailed drawings copied from old textbooks
You say she likes to sew- could she work out how to make a wall hanging or rug for her room?
She could try her hand at book-binding or puzzle making (fretwork?), or stamp collecting
She could start a collection- maybe of postcards
Candle making/melting candles into weird shapes
Papier mache- she could make a family of people
Introduce her to art- children would be responsive to the Impressionists I think, they're apparently the most accessible. Or Expressionism. Any kid would be fascinated by Chagall. Have her try to copy Michelangelo's drawings of people.
She could make a multimedia comic book, or an album if you have some photos in hard copy