Howl of the Ancients. The Matching Games, #3

She can feel her sister's magic killing her. Her sister can't feel a thing. When eighteen-year-old Sara MacArthur wins a brutal werewolf tournament, she expects politics, power plays, and a husband she didn't choose. What she doesn't expect is the gold scars spreading across her face - or the terrifying realization that her twin sister Nikki's newfound magic is draining Sara's life force through the bond they've shared since birth.
Every spell Nikki casts makes her stronger. Every spell makes Sara weaker. And Nikki can't even tell it's happening. With an ancient war-binding spell unraveling beneath their feet, a undead warlord racing them to the only book that can save them, and a shimmering dome that will only open for two sisters whose togetherness might destroy them both - Sara and Nikki must cross into a world their mother abandoned before the bond between them snaps and takes civilization with it.
But the dome has a price: the closer the twins get, the faster the bond breaks. One sister is burning out. The other is fading. And the mountains are starting to shake. Perfect for fans of Sarah J. Maas, Naomi Novik, and anyone who's ever loved someone so fiercely it hurt.