How would she have saved him? By the time she got to the railing, the guy was dead? Elijah didn’t hold her back until the man was on the ground. So I don’t see how Elijah stopped her from saving him?
She was struggling to get out, the camera shows her walking towards them, and then it only shows Rebekah again when Elijah is already holding her, we don’t know if she got there before he hit the ground, and she’s trying to get out from his hold. She has super speed, I’m pretty sure she could get down there before he hit the ground if she wasn’t being restrained. Or go make sure he really was dead the second he hit the ground.
She asked Elijah, “Dearest Elijah. You’ve only ever wished happiness for me. Emil and I are in love. Please, let me turn him.” and he says “Rebekah, the governor has graciously agreed to hide a lot of our… indiscretions. It would not do to turn his son into one of us.”.
He didn’t want Rebekah messing up whatever deal they had with the governor, and if she had saved Emil, she would have turned him for sure after Klaus tried to kill him.