Thank you for sharing this burden and for your love for your friend. It is a heavy thing to watch someone you care for face metastatic melanoma, and it is a beautiful thing that you are bringing her before the Lord in prayer.
I want to join with you in prayer for her, and to agree with you asking God for healing, for the treatment to be effective in bringing remission, and for protection from harsh side effects. The Scripture teaches that when two or three agree on earth concerning anything they ask, it will be done by the Father, and there is power when we come together in that kind of agreement from the heart. The fervent, heartfelt prayer of a righteous person avails much, not because of many words or length, but because it rises from real need and trust.
Jesus taught us to keep coming with shameless persistence, like a friend who keeps knocking at midnight until the door is opened. That persistence is not to wear down a reluctant God, but to keep our hearts open and aligned with Him. True prayer begins with God and His purposes. He puts His desires in our hearts, we offer them back to Him, and He then accomplishes His will. So we do not pray simply to get our own wishes fulfilled, but to see His will done on earth, and to open the door for Him to do what He has long desired to do without violating our will.
That is why prayer rests on relationship. When we can truly say Father, because we have come to Him through Jesus Christ for forgiveness, we have confidence to approach Him. If anyone has not yet come that way, the first and most important prayer is, God be merciful to me, a sinner, which establishes that relationship and opens the way to all other prayer.
We also know from Scripture that prayer for the sick was part of the ministry of Jesus and continued in the early church as people were brought for prayer. God still hears and still heals. At the same time, we have the example of Paul who prayed three times for relief and heard the Lord answer, My grace is sufficient for you, for My strength is made perfect in weakness. And we remember that even the prophet through whom God did many miracles still faced suffering and death. This reminds us that while we pray boldly and persistently for complete healing, we also trust God's wisdom and love if His answer takes a different form than we hope.
So let us pray together now for your dear friend, asking for God's mercy and healing touch upon her body, for wisdom for those caring for her, for the treatment to work with as little harm as possible, and above all for God's perfect will to be accomplished in her life. May she know His comfort and assurance as she prays, for often the Spirit ministers peace and strength in the very act of prayer. And may her life continue to bear fruit for His glory, whether through restored health or through the grace He supplies in weakness.
I will continue to hold her up before the Father with you, asking with persistence and trust, and resting in His goodness and power forever.