Do you have any idea what it's like to know the world has given up on you? Gem does. After she was killed in a battle and fell into the water, the only way she could survive was by the ambient magic of the sea taking her under its wing, a magic ruled by no master and constricted by no borders. She washed up ready to continue her quest against evil, but the light magic she used to wield now burns her. She knew no other way of carrying out her prophecy. But...she was going to find one! She was still working on it! A couple years is nothing in the span of what it takes to properly learn a new magic, she was still going to try.... But not anymore. Skizz is here. Her time is up. The world has given up on her.
She wishes she could pretend it's because she's undead, that the world no longer thinks she exists and therefore thought it had to replace her. There are too many other nonhumans about for that to be the case, though. No. It simply thought she failed, ignored the empty outline in its plan left by her (not empty) (still full) (why won't it give me more time, why won't it see me...?) and decided to find someone to fill it.
She's not hunting Skizz to get her role back, or out of spite. She's hunting him to teach him a lesson. She wants him to see how once he fails too, the world will throw him away, ignore everything it changed by summoning him here and simply find another hero instead. In Gem's mind, the magic and will of the land is now treacherous, and the ancient, ever-moving sea is the only thing left that's ever been loyal. Soon, she will commit Skizz to its arms and let it wash away his false hopes for him.
Soon, she will finally have a friend to join her in failure.
She may not be right - maybe Skizz will show her a new way, a way that they can fulfill the prophecy with the power of two instead of one, or even just a way of thinking that shows the land hasn't quite forgotten her. Or, maybe she will show him her side, and he'll find his solace beneath the ways. Whatever happens in the end, she certainly is determined.