All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
The words said by that woman to her husband are not considered Thihaar, and the majority of scholars are of the view that no expiation is obligatory on her, be it for Thihaar or for an oath (for those who give it the ruling of an oath). This is because the words she uttered are abominable and false, thus they do not constitute Thihaar. Thus, no expiation is required in this case, just like there is no expiation required in case of insult or slander. This is what is apparent to us regarding your question.
Based on this, we reiterate: The words uttered by that woman are not considered Thihaar, but are ill words that are false. So, their marriage is valid, and they can have sexual relation as husband and wife.
Allah Knows best.