Found two IB stories at The Overflowing Bra:
Sarah finds satisfaction
A spell has been cast on Sarah that makes her always grow more young/tall/beautiful than anyone else in the room. When she's by herself it wears off and she becomes her old dowdy self again.
The Gem of Possibilities; or What If...
Basically a wish-granting gem, and its owner uses it to make herself more and more irresistable to a certain man...
EDIT: Here are two more, previously mentioned in the Attribute Theft/Transfer thread. The first one has a little incest.
http://overflowingbra.com/results.htm?varname=474