Albert Barnes Commentary Judges 11:37

"And she said unto her father, Let this thing be done for me: let me alone two months, that I may depart and go down upon the mountains, and bewail my virginity, I and my companions." — Judges 11:37 (ASV)

Bewail my virginity - To become a wife and a mother was the ultimate purpose of life to an Israelite maiden. The premature death of Jephthah’s daughter was about to frustrate this purpose.