"the vow that she has made ... that is, the rash talk of her lips." These two phrases refer to the same thing. The second phrase describes the vow that the woman made.
"the rash things she has said" or "her rash promise". The phrase "the rash talk" refers to the rash promise that she made. Here "her lips" means the woman herself.
"Yahweh will forgive her for not fulfilling her vow". Here Moses speaks about Yahweh forgiving the woman for not fulfilling her vow as if he were releasing her from something that bound her.