Praise be to Allaah.
If a woman prays in jamaa’ah (congregation) behind her husband, he should stand in one row and she should stand in another behind him. Ibn Rushd (may Allaah have mercy on him) said in Bidaayah al-Mujtahid, 1/361):
‘I do not know of any difference of opinion about the Sunnah that a woman should stand behind the man or men, if there is another man besides the imaam, or behind the imaam if she is alone. This is known from the hadeeth of Anas which was reported by al-Bukhaari, in which he said that the Prophet (peace and blessings of Allaah be upon him) led him and his mother and maternal aunt in prayer: “He made me stand on his right, and made the woman stand behind us.” This was also reported by Maalik, according to whom he said: “I and the orphan stood behind him (peace and blessings of Allaah be upon him), and the old woman stood behind us.”’
Elsewhere he said: ‘There is no difference of opinion regarding the fact that a woman on her own should pray behind the imaam, and that if there is another man present, he should stand beside the imaam and the woman should stand behind him.”
This is the opinion of all four Imaams. And Allaah knows best.