Complex sentence: In 1203 her father Hōjō Tokimasa was appointed regent to the shōgun, Yoritomo's son Minamoto no Sanetomo, and henceforth the Minamoto shōguns became puppets of the Hōjō regents, a samurai of Taira descent, who wielded actual power.
Split into simpler sentences: In 1203 her father, Hōjō Tokimasa, was appointed regent to the shogun, Yoritomo's son Minamoto no Sanetomo. Henceforth the Minamoto shoguns became puppets of the Hōjō regents, who were samurai of Taira descent and who wielded actual power.