Book Four in the Flame Series: Consumed with Fire by Theresa Gage

Traumatized and depressed after the war with the humans, Cassie, a tree troll, must survive after she lost the majority of her clan including her brother. King Roark believes her fortress belongs to him as a war prize, but Cassie fights him at every turn and vows he will never take her property. Seeking revenge, she enlists the help from a witch, but her plan backfires after Cassie kidnaps the queen. Larkin, the queen's sister, takes it upon herself to find Cassie and puts her in the dungeon. While there, Larkin stabs Cassie's thigh and it becomes infected. Cassie later escapes, but is wanted for treason, than murder after she kills one of the king's dragons. Losing her leg from the infection, she must learn to trust others and ask for help.