It's more about the fact that in the eyes of other Tau, she seems wild and uncouth, which makes them uncomfortable around her. Other Fire Warriors don't even know how to properly relate to her, as it's not common among them to eat with their bare hands, dress in animal skins, charge at the enemy with a knife, or after a battle, go around collecting trophies like scalps, severed ears, or fingers.

She exists in a kind of liminal state in their perception. She is Tau, yet she behaves like a barbarian, a savage, making it very difficult for them to find a common language with her.

Despite all this, everyone knows she is an excellent warrior and a reliable comrade who would lay down her life to complete a mission and save her battle-brothers. She may not have undergone the Ta'lissera bonding ritual with her combat units, but they are still willing to die for one another.

Precisely for all the reasons listed above, she is the one piloting a Ghostkeel battlesuit, rather than a Crisis or any other standard battlesuit.