Well, if I recall right, then you have to black it out ( full alpha channel) and set the model's Material Filter to Transparent ( or was it Blend ?). Then there will be a .. there will be nothing where the skin originally was, though the vertices are still there.
However, as you notice, you need to edit as well the model and the skin. It would be easier to newly wrap or remove the parts you don't want Jaina to have ( for such easy/moderate issues the Request section usually helps you).
EDIT: Sorry, confused the section you posted it. The things above still apply, you simply have to draw the hole on the Jaina skin and then edit the model.