Can she withhold herself from her husband who does not pray?

Praise be to Allah.

Indeed it is obligatory for the woman (in this situation) to withhold herself from that intimate relationship, and the opposite also applies [i.e., a man should withhold himself from his wife if she does not pray]. Allaah says (interpretation of the meaning):

“… Likewise hold not the disbelieving women as wives…” [al-Muntahanah 60:10]

It is not permissible for a Muslim woman to stay with a man who does not pray at all or does not pray most of the time; she has to leave him and not stay with him, because he is a kaafir who has gone beyond the pale of Islam. We ask Allaah to keep you safe and sound.