The story of Jephthah's daughter is special to me because this issue was a turning point for me when I realized that the Bible is not holy and cannot have come from a loving Creator.
I spent a lot of time trying to explain it in a positive way for the Bible, I read many explanations from various apologists. I repeatedly begged God, in whom I still deeply believed at that time, often with tears in my eyes to give me understanding. All to no avail. All because, in my opinion, the Bible itself does not leave much room for speculation.
So when it comes to interpreting the Bible, I think the first place to look for the answer is in the Bible itself. I think the answer to this matter is in Leviticus chapter 27. This chapter contains the laws regarding making vows. Jephthah made a vow, so let's see what laws applied to him. It turns out that according to Leviticus 27, there are two types of vows: those that can be revoked (verses 1-27) and those that cannot be revoked (28, 29). If Jephthah made the first kind of vow, he could easily redeem his daughter according to the tariff (30 or 10 shekels depending on age) However, as he himself said, he could not revoke this vow: "Now I have opened my mouth to Jehovah, and I am unable to turn back.” So what did he have to do with his daughter according to Leviticus 27:28, 29? He had to burn her." But no devoted thing that a man devotes unconditionally to Jehovah from his belongings may be sold or bought back, whether from mankind or animals or the field he possesses. Every devoted thing is something most holy to Jehovah.29 Furthermore, no condemned person who is set apart for destruction may be redeemed. He should be put to death without fail."
And then there is the fact that Abraham did not at all question the source of the voice that told him to offer his son on the stake. He was sure that this is his God and not for example same evil angel who tells him to do it