We understand your concern and we are here to support you in prayer and guidance. Let us first address your situation with a word of prayer.
"Father in heaven, we come before You in the name of Jesus Christ, seeking Your protection and peace for our sister. Lord, You see the discomfort and fear she is experiencing due to her neighbor's behavior. We ask that You surround her with Your angels, protecting her from any harm or evil intent. Grant her wisdom in how to interact with this neighbor, and fill her heart with peace, knowing that You are her shield and defender. Lord, we also pray for her neighbor, that You would soften her heart and deliver her from any spirit of jealousy or envy. In Jesus' name, we pray. Amen."
We are reminded of Psalm 91, which assures us of God's protection: "He who dwells in the secret place of the Most High will rest in the shadow of the Almighty. I will say of Yahweh, 'He is my refuge and my fortress; my God, in whom I trust.' For he will deliver you from the snare of the fowler, and from the deadly pestilence. He will cover you with his feathers. Under his wings you will take refuge. His faithfulness is your shield and rampart" (Psalm 91:1-4, WEB).
In response to your neighbor's behavior, we advise you to continue to treat her with kindness and respect, as difficult as it may be. Romans 12:17-21 (WEB) tells us, "Don’t return evil for evil. Respect what is honorable in the sight of all men. If it is possible, as much as it is up to you, be at peace with all men. Don’t seek revenge yourselves, beloved, but give place to God’s wrath. For it is written, 'Vengeance belongs to me; I will repay, says the Lord.' Therefore 'If your enemy is hungry, feed him. If he is thirsty, give him a drink; for in doing so, you will heap coals of fire on his head.' Don’t be overcome by evil, but overcome evil with good."
Remember, it is only through the name of Jesus Christ that we can approach God and be saved (Acts 4:12). If you haven't already, consider sharing the love of Christ with your neighbor, as God might be using you to bring her to Him.
As for a prayer you can say, consider this: "Lord Jesus, I thank You for being my protector and refuge. I ask that You would fill me with Your peace and guide my interactions with my neighbor. Help me to show her Your love and kindness, and to respond to her actions with patience and understanding. Lord, I also pray for her, that You would bless her and bring her into a right relationship with You. In Jesus' name, I pray. Amen."
May God's peace and protection be with you.