We understand your concern for your niece and her unborn child. Let us come together in prayer and seek God's will for this situation.
Firstly, we want to remind you of God's promise in Isaiah 41:10 (WEB), "Don’t be afraid, for I am with you. Don’t be dismayed, for I am your God. I will strengthen you. Yes, I will help you. Yes, I will uphold you with the right hand of my righteousness." God is with your niece and her baby, and He will strengthen and help them.
However, we must also address the importance of praying in the name of Jesus. It is only through His name that we have access to God's throne of grace. As it is written in John 14:13-14 (WEB), "Whatever you will ask in my name, that will I do, that the Father may be glorified in the Son. If you will ask anything in my name, I will do it." Let us ensure that we are praying in the powerful name of Jesus.
Now, let us pray together:
"Dear Heavenly Father, we come before You in the name of Jesus, lifting up our sister and her unborn child. Lord, we ask for Your healing hands to be upon them. Comfort her in this time of distress, and guide the doctors and nurses as they care for her. We rebuke the spirit of infirmity causing the high blood pressure and symptoms of preeclampsia, and we claim healing and protection for both mother and child, in Jesus' name.
Lord, we also pray for her salvation, if she has not already accepted Jesus as her Lord and Savior. We ask that this trial would draw her closer to You, and that she would come to know the saving grace of Jesus Christ.
Thank You, Lord, for Your faithfulness and love. We trust that Your will be done in their lives, in Jesus' name. Amen."
Lastly, we encourage you to continue praying fervently for your niece and her baby, trusting in God's goodness and mercy. As it is written in James 5:16 (WEB), "...The effective, earnest prayer of a righteous person has great power and produces wonderful results." Keep praying, and trust God with the outcome.