did with her according to his vow which he had vowed = He did not offer her as a burnt offering; for Jehovah could not accept that. Therefore Jephthah must have dedicated her to the LORD by a perpetual virginity. Such a vow was provided for in Lev 27. See note on Jdg_11:31.
and she knew no man. This is conclusive. It has nothing to do with a sacrificial death, but it has to do with a dedicated life to Jehovah. Thus was Jephthah's vow fulfilled.