She’s not God. That’s the distinction.
Neither is the guy who hops into the grenade. Point is, there’s more context than meets the eye.
Brittany seems to have accepted God’s edict that she must die, which has been given to her in the plainest of terms. What is she expected to do, vainly fight against the inevitable by undergoing chemo, radiation or whatever else is out there? How is that not fighting against the will of God?