Welcome @JumpJockey. First of all, I'm so sorry for what you are going through with your DD. I think your child being so seriously ill must be one of the hardest things to deal with.
I'd like to offer a little of my perspective formed from my own experience, but it's not really an answer - I'm not sure there is one, really.
The first thing I'd say is please don't fall for the idea of it being a test from God. I know people say that with all good intentions, because they don't know what else to say, but God isn't like that and it's not something we find when we look at Jesus. I've come to see that it's simply that we live in a broken world, and as Christians we are not somehow immune from that.
I've had a life limiting illness since I was a small child and my parents then me went through a whole lot of this (and continue to, when I get really sick). I've wondered where God is, why he hasn't healed me, why he's left me in pain. Yet one of the things I've found most comforting in this is the raw authenticity of many Bible passages in the way they pour out their pain, too. They know that God can take it. The Psalms is full of writers crying out to God, and then when they are spent with their tears they make a decision to turn towards God and hope in God. And in my experience it's in that turning to hope that I find some kind of peace - not that things suddenly improve, but that my soul is more at rest.
I know this is not an answer as to why your dear little girl is going through all of this rubbish. But it helps me to look at Jesus as well, who went through the worst of suffering and then death because of his love for us, and so never gave up on us and also understands our pain. That's why I keep looking back to God; because of Jesus and his unimaginable love.
There's a passage of Scripture that talks about creation groaning to be made right, and that's how I feel and how I see our broken world. We are off balance, askew, we know that we are not right and we so long to be. And we have a hope in us because one day God will restore all things and make all things right.
God does answer prayers, sometimes as we hope, sometimes in incredible ways, sometimes in barely imperceptible ways, sometimes in ways we have no clue about yet. For me it's sometimes about simply knowing God is there, with me, holding my hand and weeping with me through the pain. I find a joy in God's presence despite it all and find that when I turn to God I am so often liberated from the pain that keeps me at a dark place in my soul, if not the pain in my body.
And sometimes I am not, and I wonder where God is.
But the truth is God has never left me; I simply sometimes cannot see God's work and fingerprints on my life.
I'm so sorry for what you are going through. There are no words, really, but I often find reading a Psalm aloud can help. I like Psalm 121, or 23, or 63 - but there are so many. It can help 