Instruct one of the female assistants to hide in the lower half of the wooden box before the box is rolled out onto stage.
Instruct the other female assistant to climb into the box in front of the audience, with her head sticking out of a hole at the end of the box. She will curl her body to fit in one end of the box. Once the second assistant is in the box, have the first assistant, who is hiding in the box, stick her legs out of holes in the bottom end of the box. This will give the illusion of only one lady in the box.
Saw the box down the middle, and move each half of the box so that the feet and head of the assistants are facing the audience. The female whose head is visible can smile at the crowd, while the female whose legs are visible can wiggle her legs.
Put the two halves of the box back together, open the cabinet doors, and have the female assistant, whose head was visible climb, out of the box, completely intact, to the crowd's amazement.
Insert a set of prosthetic legs on stilts into the lower half of the box before rolling the box onto the stage in front of the audience. Make sure the legs are not visible to the audience.
Instruct your female assistant to climb into the box. She will curl up her body so it fits only in one half of the box. She will pushing the fake feet out of the holes by pushing down on the stilts.
Saw the box down the middle, and move each half of the box so that the feet and head of the assistants are facing the audience.
Put the two halves of the box back together, open the cabinet doors, and have the female assistant pull the fake legs back into the box. She then climbs out of the box to reveal her full self to the audience.