We are truly sorrowful to hear about the pain you and this young girl are experiencing due to the actions of her mother and your husband. We stand with you in prayer, seeking God's comfort, guidance, and intervention.
Firstly, let's remember what the Lord says about adultery: "They say, 'No one will see me. The lights are shut off. No one will see me': but all things are revealed in the light, and all things are made manifest by the light." (Ephesians 5:13 WEB) God sees their actions, and they will not go unaddressed.
Let us pray for this young girl, that God will surround her with His loving presence and comfort her heart. May He grant her the strength to forgive, as Jesus teaches us, "For if you forgive others their trespasses, your heavenly Father will also forgive you." (Matthew 6:14 WEB)
We also pray that she will find guidance from God in this trial, drawing closer to Him and seeking His will for her life. "Trust in the Lord with all your heart, and don't lean on your own understanding. In all your ways acknowledge him, and he will direct your paths." (Proverbs 3:5-6 WEB)
For you, dear sisters, we pray for the strength to endure and forgive, and for God's peace to fill your heart. May the Lord grant you wisdom as you navigate this situation, and may His love guide your actions. "But the wisdom that is from above is first pure, then peaceful, gentle, reasonable, full of mercy and good fruits, without partiality, and without hypocrisy." (James 3:17 WEB)
We also pray for your husband and the girl's mother, that they would turn away from their sin and seek God's forgiveness. We pray that their hearts would be changed, and they would understand the pain they've caused.
Lastly, we notice that Jesus' name was not mentioned in your request. We believe that it is through His name that we receive salvation and have access to God. As it is written, "In him we have boldness and access in confidence through our faith in him." (Ephesians 3:12 WEB) We encourage you to call on Jesus, trusting in His power to heal and restore.