So far, all of the alien fixes for things have caused problems. That is very much the point; even if she's powerful and honestly doesn't seem to be trying to do anything openly bad, her failure to understand the vulnerability and fragility of human life has caused terrible consequences.Welp, even if she comes back normal, her disappearance already had irreversible damage to someone else…so that’s probably what they are going for.
But there is another point here too. Karagaki was invisible. Nobody cared about her, nobody wanted her around, nobody looked for her when she was gone, the world doesn't seem to give a single shit that she died. But Teru did, and his life was turned upside down because of it. Everyone matters to someone. Everyone will be noticed when they are gone. Just erasing someone from the world isn't possible, because no matter what somebody will notice, care, and be impacted deeply.