Learn Arabic (Modern Standard): للبنت ساقان قصيرتان.

The suffix ـان is used for the dual form when the word is the subject of the sentence. Even though 'two short legs' comes at the end of the English translation, in Arabic, 'two short legs' is the actual subject (literally: 'to the girl are two short legs'). If it were the object of an action, you would use ـين instead.

The word for 'leg' (ساق) doesn't end in a feminine ة, so why does the adjective قصيرتان have the feminine dual ending ـتان?

In Arabic, body parts that come in pairs (like eyes, hands, and legs) are naturally feminine. Because ساق (leg) is feminine, its adjective must also be feminine, which is قصيرة (short). When we make it dual, the ة opens up into a regular ت to connect to the suffix, giving us قصيرتان.

Where is the verb for 'has' in this sentence?

Arabic doesn't have a direct verb for 'to have'. Instead, it uses the preposition لـ (meaning 'to' or 'for') attached to the owner. للبنت literally means 'to the girl', so the whole sentence is structured as 'to the girl are two short legs'.

Why is it written للبنت? What happened to the alif in البنت?