QUOTE(Mad Tom @ Mar 14 2008, 04:21 PM)

There is a very nice arrangement of
Ain't Misbehavin' in
Great Piano Solos: The Black BookIf that is too difficult at Grade 6, then the same volume also has a fairly authentic sounding version of
My Baby Just Cares For Me that is a lot easier and should be doable (especially with from now to November to practice)

<-- Do .... Be Do ..... Be Do .... Be Do Beeeee Do
Depends whether she is playing jazz or not ... and whether she is playing with other people.
Forgive me for stating the obvious, but if it is a jazz gig, then some improvisation will be almost inevitable, and if she is playing with others she'll probably be comping chords rather than playing a tune. Why not learn and practice improvising on a standard - Autumn Leaves is easy, or take something from the ABRSM fake book.
If on the other hand she just needs to play a solo that sounds jazzy, then there are loads of transcriptions, and not all of them will be that hard. The Jazzwise site might be a good bet for ideas.
nick