An Execution Gown?

Clémence Poésy plays Mary, Queen of Scots in "Gunpowder, Treason and Plot" in which she wears this gown. I haven't seen the movie yet but this looks like her execution scene and if that is the case then the dress is very historically incorrect since Mary wore a deep red dress for her execution. Anyway, this dress is made of a champagne/grey satin with a simple skirt that shows no petticoat whatsoever. The bodice is trimmed with an edge of cotton ribbon. There is a twist to it though - the bodice suddenly drops at the middle of the chest to reveal the same fabric as the bodice.
On each shoulder there is a roll with the same cotton ribbon as on the bodice. The collar is stiff and almost standing (its probably resting on the rolls). Notice that the sleeves are made of a different fabric than the rest of the gown though it is kept in the same colour: the sleeves are marked with white dots and has been trimmed with cotton ribbon.