Thank you for sharing this burden for your friend and for wanting to bring her before the Lord. It is a loving and faithful thing to intercede for someone who has carried this battle with cancer for so long, especially as it has become more difficult lately.
We want to join with you in agreement in prayer for her, because Jesus said that when two or three agree on earth about anything they ask, it will be done by the Father. There is power when God's people pray together from the heart, not because of long or perfect words, but because fervent prayer from a righteous heart is effective. The prayers we see in the Bible are often very short and simple, and God hears them when they come from sincere dependence on Him.
It helps to remember what prayer is truly for. Prayer is not a way to inform God of something He does not know, for your Father already knows what is needed before we ask. Prayer is not a way to persuade a reluctant God or to make Him see things our way. The purpose of prayer is not to get our will done on earth, but to see His will done. True prayer begins with God and His purposes, He makes His will known to our hearts, and we then speak that back to Him, opening the door for Him to do what He has desired to do without violating our will. That is why the wisest prayer we can pray is, Lord, have Your way and accomplish Your perfect will in this life and in this situation. Yours is the kingdom and the power and the glory.
We also remember that prayer rests on relationship. We can come and say Father only because we have been brought into His family through Jesus Christ. If anyone does not yet know Him, the first prayer God desires to hear is, God be merciful to me, a sinner, which opens the way to all the other promises of prayer.
With that in mind we will pray persistently for your friend. Jesus taught about a man who kept knocking shamelessly at his friend's door at midnight until he received what he needed, not to teach that we must wear God down, but to show that God welcomes continual, earnest coming to Him.
So we pray for your friend that the Lord would have mercy and bring healing according to His perfect will, that He would comfort her and strengthen her in this long trial, and that He would give her and those caring for her wisdom in every decision about treatment. We understand your hope that she would consider the supplements and the red light you mentioned, and we pray that God would guide her clearly to what is truly helpful and wise, and that above any particular remedy she would know His presence, His peace, and His grace which is sufficient in weakness. As with the apostle Paul who prayed three times for his affliction to be removed and heard the Lord say, My grace is sufficient for you and My strength is made perfect in weakness, we trust that whether God brings healing in this life or sustains through the trial, He will do what is best and most glorifying to Himself.
We are praying that she will know the healing touch of Jesus, who healed the sick and whose followers in the early church brought the sick for prayer, and that she will experience His nearness and care each day. We also pray for you as her friend, that God would give you grace to love her well and to keep lifting her up with faithful, heartfelt prayer.