Numbers 30:15

30:15 But if he should nullify them after he has heard them, then he will bear her iniquity.” ¹ 

Numbers 32:12

32:12 except Caleb son of Jephunneh the Kenizzite, and Joshua son of Nun, for they followed the Lord wholeheartedly.’

[30:15]  ¹ sn In other words, he will pay the penalty for making her break her vows if he makes her stop what she vowed. It will not be her responsibility.