Jehovah's witnesses insist that Jephthah did not sacrifice his daughter to Jehovah. This is important to them because, rarther than Jephthah just being a random bad person, Jehovah was very much in on the deal. After all, he made the promise to Jehovah that he would "offer up as a burnt offering" on his return the first thing to come out of his house if Jehovah would give the Ammonites into his hands in Battle, and since they were this makes Jehovah complicit.
The Isrealites had been getting a good thrashing of late, and the Gilead Elders (Oh boy) had come out to ask Jephthah, the rejected son of a prostitute (wouldn't you know it) and renown soldier, if he would lead the Isrealites into battle for them.
This is when Jephthah makes the deal with Jehobo, and it all centres on the word for "burnt offering", which is given as "olah". Now "olah" is used two other times in the Bible. Interestingly, on both occasions someone was gonna get a roasting - the first time when Abraham offers to sacrifice Issac to Jehovah, and the second time when Saul threatens to sacrifice Johnathan. This time to placate Jehovah, since Johnathan had broken a rule on fasting after a fortunate outcome in battle. Saul feared that without a human offering Jehovah would be too angry to allow them to complete their winning streak.
On both Occasions God, or man, intervened to prevent the offering. In the case of Jephthah, his daughter requested two months grace to bewail "her virginity", you would think that someone in that time could have worked out a deal to stop it! And why was Jephthah offering the first thing "out of his house"??? He must have known it was at least likely to be human, which makes you think human sacrifice wasn't unheard of amoung the Isrealites, if they wanted something from God badly enough, that is.
The witnesses insist that this daughter was merely offered up in a spiritual sense, to serve at the temple, perhaps.They claim she went to bewail she would not marry- not her impending death. But since the Jews at that time had no concept of an afterlife, or any life, but this one, having children meant, essentially, your immortality. To this day having children is incredibly important to Jews. Since she was Jephthah's only child, it meant he too would have no descendents to mourn him.
As to the Witness interpretation, the guys who wrote the Hebrew scriptures aren't having any of it. The modern Jews completely accept this was a human sacrifice. They know that their word "olah" means one thing. In fact I believe it's the root of the word "holocaust", coined by author Ellie Weisel, an "offering up" of the Jewish people. Despite scriptures prohibiting the practice, like polytheism, human sacrifice was definately practiced by ancient Isrealites, and there is evidence of both scattered throughout the Bible.