Okay, let me come at this question another way...couldn't it also be the prerogative of God not to provide total healing if it furthers His cause of spreading the gospel-The Great Commission? The example I am thinking of is Joni Eareckson Tada. She has been a paraplegic for over 40 years now, but through her disability and her submission to God's will for her life thousands, perhaps millions, around the world have come to know Christ. She has an international ministry that is dedicated to the "spiritual healing" of those who are disabled and their families. She has the unique opportunity to do mighty things for the LORD with what the world views as a "damaged" body.
The way I see it, it is when we are at our most vulnerable and painful state that God's power in us is that more apparent. Another example is the Apostle Paul. God never removed that thorn in his flesh (some say it was an eye illness) that tormented him. [II Cor. 12:7-10] Yet Christ used him to spread the Gospel to the Gentiles and to write a good portion of the New Testament. Vs.9 "My grace is sufficient for you, for my power is made perfect in weakness."
If so many people have come to the knowledge of the Truth through her sickness, how many more through her healing? Sometimes people are a certain way so that God might show his glory through them, yet it has never been his will for anyone to be sick. Sickness is of Satan, not of God. Some people are sick because of sin, but some are sick so that they might be healed to show God's glory. Either way If people are coming to Jesus Christ, Amen, but don't glorify sickness to say her sickness brought people to Jesus. The Holy Spirit brings people to Jesus Christ.
Now, if she says spiritual healing then she must have also seen the manifestation of this healing, because what is done in heaven, is done on earth for those who are in Christ to manifest his glory here on earth. Does she give glory to Spiritual healing or to God who heals, or to her sickness? God doesn't make us weak to show his glory. But when we are weak we are more able to behold his glory. because we are evidence to ourselves that we cannot do his perfect will alone. Mighty things for the Lord will not save anyone. Many people will present their mighty things before the Lord on judgment day and he will say to them, I never knew you you worker of iniquity. They will say, haven't we done this... or haven't we done that... in your name, but he will say depart from me you that works iniquity. Who is getting the glory? Whose is the Power? Whose is the Kingdom?
Jesus said, the ones who are his disciples will cast out demons and lay hands on the sick and they will be healed, and take up serpents that, if they bite them will not harm them. But whose power is it? THE POWER AND GLORY AND HONOR IS GOD'S not her sickness. If she uses sickness as a means to get sympathy for God then she has erred. The gospel OF JESUS CHRIST is the ONLY POWER OF GOD unto salvation. Not the gospel of Ramon, nor the gospel of Paul, nor the gospel of Joni Eareckson Tada.