[coliveira]

> he could have repented and received grace and he still would have had his daughter.

This is just modern people creating a new interpretation of old writings. Apparently Abraham also didn't know about the "grace", since he was decided to kill his son and didn't even tried to ask God otherwise. God also was not worried at all, since he didn't care to enlighten Jephthah about his "grace" (even for the sake of the child).