We are truly sorry to hear about the situation your daughter is facing. We will stand with you in prayer and provide some biblical guidance.
The alcoholic fiancé has no sacred rights to your daughter. The Bible says "What God has joined together, let no man separate." (Matthew 19:6). But in this case, they are not married. If the fiancé is not living according to God's moral standards, it's important for your daughter to seek the right path with God. We should pray for the fiancé for healing from alcoholism and Godly behavior. According to 1 Corinthians 6:9-10, drunkards will not inherit the Kingdom of God.
Firstly, let's pray for your daughter's safety and peace. "Do not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, present your requests to God. And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus." (Philippians 4:6-7 WEB)
Let's pray for your daughter's needs and to be protected from the fiancé. "And my God will supply every need of yours according to his riches in glory in Christ Jesus." (Philippians 4:19 WEB)
Let's pray for the fiancé to be forgiven, convicted of his wrong behavior, and transformed to become a godly man. "In the same way, you wives, be in subjection to your own husbands; so that, even if any obey not the word, they may without the word be won by the behavior of their wives; seeing your pure behavior in fear." (1 Peter 3:1-2 WEB) It is our prayer this verse can come true as both of them remain unmarried at this time.
Let's pray for your daughter to have wisdom and discernment in this situation. "If any of you lacks wisdom, let him ask of God, who gives to all liberally and without reproach, and it will be given to him." (James 1:5 WEB)
We must also address that your daughter should only be in a courtship with this man if he is a Christian and the goal is a Godly marriage. "Do not be unequally yoked with unbelievers, for what fellowship have righteousness and iniquity? Or what fellowship has light with darkness?" (2 Corinthians 6:14 WEB)
Lastly, we appreciate you prayed in the name of Jesus. It is only by His name we have access to God. "Jesus said to him, I am the way, the truth, and the life. No one comes to the Father, except through me." (John 14:6)
Heavenly Father, we come before You in the name of Jesus, lifting up our sister and her family. We pray for Your protection and peace over them, especially her daughter. Lord, we ask You to convict the fiancé of his sins and transform him into a godly man. We pray for Your provision and guidance in their lives. In Jesus' name, we pray. Amen.