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. If she spent years eating potatoes, wearing rough wool, sleeping on rough mattresses and harvesting squash, I can understand a personality shift once she's back in the Tower & able to partake in luxuries, where she prefers rare delicacies, elegant clothing and being more upfront in her desire for creature comforts.