A conditional permanent resident (a person with a two-year Green Card) must file Form I-751 to remove the condition within the 90-day period before the person's conditional Green Card expires. If the person is divorced at that time then she should request a waiver of the joint filing requirements, and submit both an explanation of her circumstances and documentation that she entered into the marriage in good faith. If that is necessary, it is a very good idea for her to get help from an immigration lawyer.