Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

In the Name of Allah, the All-Merciful, the Mercy-Giving

 All praise is due to Allah. Peace and blessings be upon His Messenger Muhammad.

If the wife witnessed her husband committing adultery, then she may seek dissolution of marriage; it is a legitimate ground for divorce. Restoring to li’aan (curse prayer)  is not an essential condition for marriage dissolution. However, if she wants to do that, she is free. it is wrong to say the rules are different for men and women.

She is free to do so either verbally or in writing. If he refuses to let her go, she should resort to the court system; never mind that the only option for her is to go to a secular court.

Almighty Allah knows best.