The Winter Queen — Devin Cary

The King Is Dead
The northern kingdom of Albor is in mourning. The realm's benevolent ruler has fallen victim to a fatal accident. Under his reign, Albor has known peace and prosperity, and all the denizens fear that time has come to an end. The king's son is too young to assume the throne, and a regent must be chosen to rule until the prince comes of age. With his dying breath, the king chooses his wife--Queen Elissa.

Long Live the Queen
Elissa isn't prepared to become regent, but she must if her children -- the prince and the princess are to survive the machinations of the kingdom's lords and nobles. They will never accept a woman on the throne and will do anything to usurp her power. But the aristocracy of Albor is unaware of just how much power Elissa possesses. Descended from a family of mages, she secretly practices her skills in sorcery.

But she can't completely control them...