Wa `alaykum as-salam wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
It is permissible for women to observe i`tikaf. It is reported that the Prophet’s wives (may Allah be pleased with them) performed i`tikaf even after the Prophet had passed away (Al-Bukhari and Muslim).
In his response to your question, Sheikh Muhammad Nur Abdullah, former president of ISNA (Islamic Society of North America) and member of the Fiqh Council of North America, states:
The last 10 days of Ramadan are an opportunity for every Muslim to have his or her sins forgiven and to gain Allah’s mercy and great rewards. One of these days is Laylat Al-Qadr, which is better than a thousand months. It is a sunnah of Prophet Muhammad (peace and blessings be upon him) to perform i`tikaf (spiritual retreat in the mosque) during the last third of Ramadan.
I`tikaf is a spiritual retreat in the mosque where the Muslim secludes for the purpose of purifying his or her heart and getting close to Allah by performing extra acts of worship, especially tahajjud (optional night prayers) and reciting Qur’an.
I`tikaf can only be done in the mosque according to the view of most scholars. Allah specifies the place for i`tikaf by saying, “but do not associate with your wives while you are in retreat (i`tikaf) in the mosques.” (Al-Baqarah 2:187)
Women can make i`tikaf just as men can. It is reported that the Prophet’s wives (may Allah be pleased with them) performed i`tikaf even after the Prophet (peace and blessings be upon him) had passed away (Al-Bukhari and Muslim).
Allah Almighty knows best.