A few thoughts. First of, depending on the context and length of time you have in front of your audience, four personalities may be difficult to convey well. I also wonder if a mute little girl will come across well in a short period of time. That said I think you are on the right track. I would consider making one character 'normal', then switching between one that is scared and timid (your little girl character) and one which is psychotic and very aggressive. I think doing much more in a short period of time would be very difficult.
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