Why is there no article in front of "tiara"? Is it a mistake?
You're correct. Normally, the article "the" would be placed in front of "tiara" here. However, in casual conversation native speakers often have the habit of dropping the article if it is at the beginning of the sentence. Additionally, it is a short and general statement, so the speaker has chosen to drop the article "the" here. Ex: Ouch. [The] coffee's too hot. Ex: Look! [The] train is coming.