Is it permissible for a wife to conceal from her husband her lack of orgasm during intercourse, and what is the ruling on that?

If a woman conceals a certain matter from her husband, there is no sin upon her, but her responsiveness to him in such matters is part of good companionship. Modesty should not prevent a woman from asking about what she needs concerning matters of her religion. Aisha, may Allah be pleased with her, said: "How excellent are the women of the Ansar; their modesty did not prevent them from seeking understanding in religion." Modesty does not impede the pursuit of knowledge, as evidenced by the Hadith of Umm Sulaym when she asked the Prophet, peace and blessings be upon him, about a woman's ghusl (ritual bath) if she experiences a wet dream.