A different take. I like it.
Jephthah did not offer his daughter in sacrifice
Jephthah's vow was not a promise to kill the first one of his household who met him after his victorious return. He did not promise to burn that person in the fire of a pagan altar. His vow was to dedicate entirely to God anyone who met him first after his victory over the sons of Ammon.
In dedicating his daughter completely to God, Jephthah was depriving his only child from marriage. In doing this he was giving up his only possibility of having descendants. This was the reason for his great anguish expressed in Judges 11: 35, when he realized that his daughter was the one that met him first.