Three Daughters of the Gemstone by Colleen Jinx-Cannon

Three sisters from three different countries are forced to unite by an alien intruder.  It is discovered they hold the power of the Gemstone and can use it to destroy an evil queen in a galaxy far away.  The girls are reluctant to fight for a cause outside their universe; until they discover the alien recruiter is none other than their father and he deliberately engineered them to be weapons against the Queen…their grandmother.