Is it permissible for a woman who performed Istikhara and divorced her husband, then regretted her decision, to go back and try to return to him, taking into consideration the saying, "He who seeks guidance [from Allah] will not be disappointed"?

A woman does not decide divorce; rather, it is in the husband's hand. She may request it from him or refer the matter to the court if she is harmed. If she means that she possesses the right to divorce, then this is an error. If she means that she requested it without a legitimate reason, then this is an error, according to the hadith: "Any woman who asks her husband for divorce without any [legitimate] cause, the fragrance of Paradise will be forbidden to her." If you request a divorce due to harm and your husband divorces you, then there is no blame. Istikhara (seeking guidance from Allah) is not permissible for forbidden things. Your reconsideration of divorce does not contradict istikhara; rather, it is one of its outcomes. Striving to restore marital life is a commendable endeavor.