Here are three ideas geared to different skill levels -- from rank beginner to rock-solid good cook. Since the class is ladies only, I suggest chocolate as a "can't go wrong."
Chocolate truffles: A very useful skill to have for a variety of purposes. You can decorate with orange, zig-zag piping for a traditional Halloween look.
Dia del muerte mousse au chocolate made with Mexican chocolate and dark rum: Everyone loves chocolate mousse, but it's an idea that's gone somewhat out of fashion. Bring it back from the dead without explanation or apology -- like Dracula in a Peter Cushing/Hammer film. You might want to think about some dia del muerte decoration if it's not to late to find them in your neck of the woods (it never is in mine). Mexican chocolate has sugar, cinnamon, vanilla and almond already in it and a slightly grainy texture. With a little more best vanilla and some smooth dark rum like Brugal, it makes a superb mousse.
Souffle au chocolate with creme anglaise: If you've got a wide, deep streak of sadism, there's nothing more fun to teach a cooking class than souffle. There are three highly technique-dependent places to screw up royally (folding, marking the top hat, and getting in and out of the oven), so the tension is incredible.