The Amethyst Crown by Kristy Dixon

Dree never thought she’d return to her life as a royal, but after working on a farm with Sen for the past two years, she receives some shocking news—her father and brother have both been killed.
Now, Dree is next in line to take the throne, but when she hears thatthe council is plotting to have her marry the repulsive captain of the king’s guard, she takes matters into her own hands and obtains a marriage contract with the grouchy farmhand Mace… after Sen turns her proposal down.
When the magical amethyst crown goes missing, Dree and Sen chase after the pirate thieves while Mace attempts to unmask the true villain back at the castle. Reunited with old friends, Dree discovers new allies in the most unlikely of places and learns that believing in love may not be so difficult after all… if she isn’t too late.

Every kingdom has its crooked leader, and this one demands to rule… or kill them all.