As a strange life form whose body was made of mineral materials, Estella's anatomy was very different from that of a human despite her humanoid form; thus, she had no such thing as vocal cords. The only sound that Estella produced was a beautiful whistle, very similar to the song of certain birds.
Broadly speaking, if one left aside specific, more complex details, Estella was a household fairy, a familiar creature in European folklore. In addition to attending to household chores, her only hobby was tending the garden and whistling.
One could imagine that a creature like Estella would have the same social skills that a statue would have. No matter how beautiful and curious Estella's appearance was, she had zero communication tools.
All this led to a very uncomfortable situation at the entrance of the Astryd residence, where a confused Estella whistled nonstop, trying to get the pair of sisters, Silvia and Samantha, out of their daze.
