It is also possible that since Leah gave thanks and praised for the good that befell her, and therefore she named him Yehuda (Genesis 29:35), Yehuda received from her the strength to acknowledge the truth, which led him to rectify the sin of selling Yosef. Through this, the sea was split. Therefore, it is stated in the feminine form "היתה" to hint at Leah's part in rectifying the sin.