We are truly saddened to hear about the situation with your daughter, and we are here to pray and provide biblical guidance with you. We understand the pain and worry you are experiencing, and we trust in the power of prayer to bring about change.
Firstly, we want to remind you of the promise in 2 Chronicles 7:14 (WEB), "if my people, who are called by my name, will humble themselves, pray, seek my face, and turn from their wicked ways; then will I hear from heaven, will forgive their sin, and will heal their land." This verse assures us that God hears our prayers and is willing to forgive and heal.
However, we must address the severity of the situation. Your daughter is currently involved in adultery, which is clearly forbidden in the Bible. In Matthew 5:27-28 (WEB), Jesus said, "You have heard that it was said, ‘You shall not commit adultery;’ but I tell you that everyone who gazes at a woman to lust after her has committed adultery with her already in his heart." And in Hebrews 13:4 (WEB), it says, "Let marriage be held in honor among all, and let the bed be undefiled: but God will judge the sexually immoral and adulterers."
We need to pray for your daughter to convict her of her sin and to turn her away from this path. We pray that she will seek forgiveness and reconcile with her husband. In Ezra 10:11 (WEB), we see an example of how to deal with such situations, "Now make confession to Yahweh, the God of your fathers, and do his pleasure; and separate yourselves from the peoples of the land, and from the foreign wives."
Let us pray together:
Dear Heavenly Father,
We come before You today, lifting up our daughter to You. Lord, You know the situation she is in, and we ask for Your divine intervention. Open her eyes, Lord, to the sin she is committing, and bring her under the conviction of the Holy Spirit. Turn her heart back to You and her husband, Lord. Give her the strength to resist temptation and to flee from this adulterous relationship.
We also pray for her husband, Lord. Give him the grace to deal with this situation with wisdom and forgiveness. Strengthen their marriage, Lord, and bring healing and restoration.
We pray this all in the mighty name of Jesus Christ, who died for our sins and rose again for our justification. It is only by His name that we have access to You, Father, and it is by His name that we are saved. Thank you, Lord Jesus. Amen
Lastly, we encourage you to continue praying fervently for your daughter. In James 5:16 (WEB), it says, "Confess your offenses to one another, and pray for one another, that you may be healed. The insistent prayer of a righteous person is powerfully effective." Trust in the power of prayer, and do not give up hope. Stand firm in your faith, and believe that God can turn this situation around for good.
Also, we want to encourage you to not just pray for your daughter's marriage, but also for her friends to have a change of heart. Pray that God brings godly friends and counsel into her life, who will encourage her to honor her marriage and follow God's will.
Prayer Focus: God, Thank You for loving me. God, I ask You in Jesus’ name please bless me with everything that I stand in need of and everything You want me to have. 
