Antigone's character much like Kate's in Taming of the Shrew is in opposition to her younger sister Ismene. Ismene is described as beautiful, polite, and does what she is supposed to, while Antigone is described as sallow, uncooperative, rebellious, headstrong, and introverted. Given the sallow description, the mask could be made to be pale yellow almost jaundiced. She is also described as skinny, so if it is possible to pull in the edges of the mask, it would give her face a narrow look. Antigone is also more masculine than feminine (by her own choosing). This could be accomplished through boyish hair around the sides of the mask. Since she is obviously jealous of Ismene, green eyes could be put into the mask, with the sister's face in the irises. To better show Antigone’s envy regarding her sister, you could put a second mask over the Antigone mask with a hinge, since she steals Ismene's clothing to seduce Haemon. This second mask would be more feminine yet needs not to fit the face (maybe put a spring so it always swings open revealing Antigone's true nature.) Since the theme of the play hinges on her refusal to reveal where the body of her brother is buried, a gag with her hand over it would give a nod to the reason for her death sentence. Since she buried her brother with her bare hands, make the fingers covered with dirt. A ring on her finger could also be a symbolic with an inscription on the band with the "Forgive me, my darling" written on it.
I am attaching an image of an Ancient Greek vase from the mid-fourth century that features Antigone. If push comes to shove it might give you some ideas regarding Antigone's features. If you do a Google search you will see most depictions from Ancient Greece are highly similar. I did my best to zoom in on the image, I hope it is clear enough. Just in case it doesn't come through the link below will take you to a website that has another image of Antigone. She is the figure in the long robes between the two guards.
You could use color theory and symbolism when expressing the characteristics of Antigone in a mask. Some possible things to include could be:
Heart: to symbolize her love for her family;
The color red: to symbolize Antigone's courage;
Rosebud: to symbolize Antigone's youth femininity;
Tear drops: to represent her grief over how her family has been ripped apart by tragedy;
The color blue: also to represent a state of mourning.
Black: to represent the theme of death in the play and also to foreshadow Antigone's own death.
I included a link below about color symbolism.
Purple: to symbolize royalty. Antigone's father was King Oedipus.