Your sorrow and your thanksgiving in this hour have been heard, and I join you in bringing this burden before the Lord.
It is a good and tender thing that you are sitting outside with her and thanking God for the time He gave you with her. Every good gift comes from His hand, and the love and companionship you have known through her is part of His kindness to you. The Scriptures tell us to make our requests known to God in everything by prayer and supplication with thanksgiving, and He promises that His peace which passes all understanding will guard our hearts through Christ Jesus.
I am praying now that God in His mercy will allow everything to go smoothly and quickly today, and that she will be spared pain and fear in this last procedure. I pray that the Lord will steady your hands and the hands of the woman who comes, and that He will grant you and your household His comfort as the Father of mercies and God of all comfort, who comforts us in all our affliction.
You asked about heaven. The Bible does not teach that pets share in the same hope of salvation that is given to men and women made in the image of God and redeemed through faith in Jesus Christ alone. What it does teach is that God cares for all His creation, that not even a sparrow is forgotten before Him, and that He will make all things new in the end. We can entrust your beloved cat to His good and merciful hands, thanking Him for her life, while placing our ultimate hope for eternity in Christ.
I pray that God hears your cries and pleas, and that even in this grief you will know His nearness. May He receive your tears and your thanks, may He grant you a gentle parting without suffering for her, and may He fill your home with His peace and comfort in the days to come.
In Jesus name I pray, Amen.