New Defender's Study Bible Notes
11:38 two months. If his daughter were to die, as many interpret this passage, Jephthah would never have sent her away from home for her last two months. It is obvious that they loved each other very much and would not want to be separated under these conditions. This interpretation is clearly wrong.
11:38 bewailed her virginity. Jephthah’s daughter would have bewailed her coming death, not her virginity, if she was to be sacrificed. Rather, she bewailed the fact that she would have to live her whole life without husband and children, merely performing service to the Lord, presumably in some menial capacity at the tabernacle. Yet she was willing to do this, because of her father’s vow and her gratitude to the Lord for His deliverance of her people from the Ammonites.
11:39 according to his vow. Note this does not say that he offered her as a burnt offering, merely that she “knew no man” throughout her life, in accord with her father’s vow.