Is the marriage of this girl valid, with her husband's knowledge and her commitment to prayer, or does her failure to maintain prayer affect the validity of the marriage?

The marriage contract is valid because it was concluded while she was praying. Abandoning prayer sometimes is a serious matter, and the husband must advise his wife and urge her to maintain prayer and supplicate for her, for Allah has obligated him to save his family from hellfire. Scholars have stated that whoever maintains prayer but allows his family to neglect it will be resurrected on the Day of Judgment among those who neglected prayer.