Offering Tahajjud (optional late night Prayer) in other than Ramadan is not permissible in congregation continuously; rather, each person has to offer it individually. However, it is permissible for your wife to offer Salah beside you as long as you do not lead her in Salah and she does not follow you. Also, there is no harm for her to offer Tahajjud with you in other than Ramadan occasionally but not continuously; because
Ibn `Abbas (may Allah be pleased with them) offered optional night Salah with the Prophet (peace be upon him) and so did
Abu Al-Darda' who offered Salah with
Salman (may Allah be pleased with them). Your wife should stand behind you when you lead her in Salah.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.