Old Magic - Rogues of Magic Series, #4

Urien has been defeated. but now there is a greater threat. Ann has barely escaped the wrath of the elders with her life and magic intact. It was all worth it. She has her brother back, but now another family member needs her help. Her grandmother, Mercury, is missing and an old enemy has taken control of her lands. Ann refuses to believe they're too late. When she and the other rogues go to investigate, they discover Mercury is still alive and long-dead secrets are finally coming to light.
Not only can she find her grandmother, but the answers they uncover could hold the key for why the elders have hunted her for so long.