Stick a cocktail stick into the pumpkin (without pushing through to the other side!).
Fix the body onto this stick. Add on a piece of solid-color Fimo glitter purple clay, creating folds in the dress. Make a roll of Fimo Glitter Purple for the arm, stick it to the dress, marking out the elbow.
To the very end of the arm, add a little 'flower-shaped' hand in Fimo Sahara. If the hand needs to grip a cocktail 'broomstick', add the hand before baking the figure.
Make the shawl collar out of Fimo Black clay. It will need to be given a 'folded' look and should cover the upper arm. Tiny petals in glitter gold clay, arranged three at a time, decorate the shawl.
Why not add a bow tie?
NB: don't forget the fastening! Unless your witch is in a sitting position, you need to make something from which to hang it before the baking stage, a piece of bent steel wire pushed into the aluminum foil ball at the back will work well (the fimo clay witch, once it's baked, is very light.)