Burnt Skies

The sunstone and moonstone are both polar opposites so when Rapunzel said the decay incantation, in reality, she was never supposed too. Now, 4 years later, the incantation itself is spreading like wildfire throughout Rapunzel's body and as time keeps ticking, the weaker and closer to death she gets. How will Cassandra save the princess before it's too late? (More but word limit)