Let's bring this matter to the Lord in prayer, trusting in His mercy and guidance. First, it's crucial to address the sin that occurred. Gambling is a form of greed and idolatry, which is forbidden in scripture. Your sister took money that was not hers and used it for personal gain; this is called stealing and is a direct violation of God's commandments.
For you know this, that no sexually immoral, nor idolater, has any inheritance in the Kingdom of Christ and of God. Let no one deceive you with empty words. For because of these things, the wrath of God comes on the children of disobedience Ephesians 5:5-6 WEB.
Those who are in sin and do not repent will not prosper. The good news is that God is forgiving, and He wants us to turn from our sins and come to Him.
For thus says Yahweh, Sing, barren, you who did not bear; break forth into singing, and cry aloud, you who did not travail with child: for more are the children of the barren, than the children of the married wife, says Yahweh. Enlarge the place of your tent, and let them stretch forth the curtains of your habitations; spare not, lengthen your cords, and strengthen your stakes. For you shall spread aboard on the right hand and on the left; and your seed shall possess the nations, and make the desolate cities to be inhabited. Isaiah 54:1-3 WEB
Don't be afraid; for you shall not be ashamed: neither be confounded; for you shall not be disappointed: for you shall forget the shame of your youth; and the memory of the widowhood of your marriage shall you remember no more. For your Maker is your husband; Yahweh of Armies is his name: and the Holy One of Israel is your Redeemer; the God of the whole earth shall he be called. For Yahweh has called you as a wife forsaken and grieved in spirit, even a wife of youth, when she is cast off, says your God. For a small moment have I forsaken you; but with great mercies will I gather you. In an overflowing wrath, I hid my face from you for a moment; but with everlasting loving kindness will I have mercy on you, says Yahweh your Redeemer. Isaiah 54:4-8 WEB
Father, we come before You, lifting up this dear ### and her family. We know that You are merciful and forgiving, and we ask for Your grace to be poured out on them. They may be dealing with heavy conviction right now, help them to repent and turn from their wicked ways so that they can receive Your forgiveness. Help this young woman to confess her sins to her employer and to take responsibility for her actions. Guide her on the right path, and give her the strength to face the consequences of her actions. Remove any negative thoughts that may be overwhelming her.
We also ask Lord, that you help this family to look at the seriousness of sin. If they are not born again, believing in the name of Jesus Christ, we pray that they will accept Jesus as their Lord and Savior and become a new creation in Him.
Jesus answered, I am the way, the truth, and the life. No one comes to the Father, except through me. John 14:6 WEB
For whoever will call on the name of the Lord will be saved. Romans 10:13 WEB
because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For with the heart man believes resulting in righteousness; and with the mouth he confesses resulting in salvation. Romans 10:9-10 WEB
Finally, help them to grow in their faith and to trust God. Help them to learn from this experience and to live according to God's will.
Prayer Focus: God, Thank You. Thank You for loving me. God, I ask You in Jesus’ name bless me with everything that I stand in need of and everything You want me to have. Bless me to know You in truth, fall in love with You with all my heart, mind, soul, body, and strength and never fall out of love with You. Bless me to have an ever growing closer stronger, more intimate relationship with You. Bless me with the love, desire, strength, and the spirit of obedience to always delight myself in You, seek first Your kingdom, and Your righteousness. Help and strengthen me God to always respect and obey You. Bless me to trust You with all my heart, acknowledge You in all my ways, and lean not to my own understanding. 
