At no point does God say "hell yeah". That account is written in a book that's essentially "what not to do".

Judges 11:29

Then the Spirit of the Lord was upon Jephthah, and he passed through Gilead and Manasseh and passed on to Mizpah of Gilead, and from Mizpah of Gilead he passed on to the Ammonites.

God was already with Jephthah before he decided to be so extra and decided to sacrifice the first thing that came out of his house. (not his daughter). Then he took his vow very literally. There was no need to try and work for such an outcome to begin with, when it was already in God's hands.