Complex sentence: On her 15th birthday, Sentinels controlled by Onslaught destroyed her apartment, killing her parents and friends, and for weeks Hallie hid in the ruins of the city with several children she rescued.
Split into simpler sentences: On her 15th birthday, Sentinels controled by Onslaught distroyed her apartment, killing her parents and friends. For weeks Hallie hid in the ruins of the city with sevreal children she rescued.