What makes Liesl seem less ugly to Dunstan?

From the text:

Liesl became less ugly after an hour or two. Her clothes were like a man’s in that she wore a jacket and trousers, but her shirt was soft and her beautiful scarf was drawn through a ring. If I had been in her place I should not have worn men’s patent-leather dancing shoes—size eleven at least—but otherwise she was discreet. Her short hair was smartly arranged, and she even wore a little colour on her lips. Nothing could mitigate the extreme, the deformed ugliness of her face, but she was graceful, she had a charming voice, and gave evidence of a keen intelligence held in check, so that Eisengrim might dominate the conversation.