Eliezer asks:
Even though the Torah allows for the addition freedom of an Amah from the words "v'Yatzah Chinam Ein Kesef", how do Chazal know it means with signs of maturity and not some other way to become free?
Eliezer, Israel
The Kollel replies:
The Torah writes "v'Yatz'ah Chinam Ein Kasef" to teach a new way for an Amah to go free.
The Mechilta on this verse (usually printed with the Malbim) brings a comparison between the father's jurisdiction over his daughter and the Adon's. Just as when she changes to be a Bogeres she leaves her father, so, too, she leaves the Adon, afterwards, because there are two extra phrases, so she leaves at the stage of Na'arah.
All the best,
Reuven Weiner