We are truly sorry to hear about the trials you are facing with your service dog and the loss of your Lab. Our hearts go out to you in this difficult time.
Firstly, let's address the concern about God's role in this. It's important to remember that God is not the author of sickness or suffering. In fact, it is because of sin entering the world that we have disease and death (Romans 5:12, WEB). God is good and merciful, and His desire is for us to live in a world without pain or suffering. But this world is fallen, and unfortunately, bad things can happen like sickness to us and our pets. Jesus did not promise us a perfect, pain-free life, but that He would be with us in the pain and difficulties of life.
But Jesus did promise those believing in Him that we would have eternal life. "For God so loved the world, that he gave his one and only Son, that whoever believes in him should not perish, but have eternal life" John 3:16 WEB. But we need to believe in Jesus to have eternal life.
We also need to be careful and be aware that sickness and death entered the world because of sin, Romans 5:12 and Romans 6:23. We also need to be aware that it is only through belief in Jesus Christ that we have access to God the Father. It is only through Jesus that we are saved and can have eternal life. "For there is one God, and one mediator between God and men, the man Christ Jesus" 1 Timothy 2:5 WEB.
But in this life, we need to remember that we can cast all our anxieties on Him, because He cares for us (1 Peter 5:7, WEB). In times of doubt and despair, we can come to Him openly and honestly, pouring out our hearts to Him as the psalmists often did. God can handle our questions and our frustrations.
Let's pray for your service dog and for your heart as you navigate this difficult time:
"Heavenly Father, we come before you today lifting up this beloved service dog. We ask for Your healing touch on her body, that if it is Your will, this cancer would be eradicated completely. We ask for Your comfort and peace for her owner, who is grieving and struggling with doubt. We pray that You would draw near to her (James 4:8 WEB), remind her of Your unfailing love and faithfulness. Help her to remember Jesus Christ and the sacrifice He made to save her and for her to have eternal life with Him. We pray that she will be comforted in this life, but also look forward to an eternity with Jesus and no pain.
We thank You, Lord, for the gift of pets and the joy they bring to our lives. We ask for Your mercy and grace in this situation. In Jesus' name, we pray. Amen."
Take heart in the words of Psalm 34:18 (WEB), "Yahweh is near to those who have a broken heart, and saves those who have a crushed spirit." God is near to you in this time of need. Keep crying out to Him and trusting in Him, and remember Jesus and His sacrifice for you and your sins. Keep praying in Jesus' name for your pet.
Prayer Focus: God, Thank You for loving me. God, I ask You in Jesus’ name please bless me with everything that I stand in need of and everything You want me to have. 
