She has a basic hairstyle, wears very basic clothing when attending the Forsaken tea parties, and her way of speaking is not coarse - it's actually quite pedantic. If you read the chapter where she is speaking to Moridin, she verges on philosophy when she appeals to a code of honor that ought to exist amongst the Forsaken.

Also, keep her personality in mind: Mesaana has never been interested in the appearance of power, she prefers real power. So Tsutama is too flamboyant for Mesaana to easily mimic.

I think the most likely cause of Tsutama's coarse language is her time on the farm, and the length of her penance.