Complex sentence: Emma put some in the onion rings she gave Zelena, to accelerate her pregnancy; she wanted baby Robin out of the way, so she could put the Darkness into Zelena and then kill her with Excalibur.
Split into simpler sentences: Emma put some in the onion rings she gave Zelena, to accelerate her pregnancy. She wanted baby Robin out of the way so she could put the Darkness into Zelena and then kill her with Excalibur.