As said in other solutions you will need to unlock 8 diffrent versions of Elizabeth swan. Altho not need i will list them again just for clarification.
The 8 you need are:-
Elizabeth swan - Normal
E.Swan - Undergarments, Redcoat, Trader, Pirate
Captain Elizabeth - normal
Captain Elizabeth - Robes.
Whats not said in other solutions is that you will unlock this cheevo naturally through gameplay.
You should unlock the last Elizabeth charachter before finishing film 3 At world's end(privided you complete the films in order that is) and you will not need to purchase anyone either.