In the end I chose to tell Ciri that her father wanted to see her again, to talk to her. Then when she asked me for my opinion I told her that it was her decision. She didn't budge, she's stubborn, so she again pushed for Geralt's opinion. Geralt told her what he thought about Emhyr. He told Ciri that he was afraid that he might manipulate her into becoming Empress. And you know what? He was right.
In this world, in all worlds, there will always be war. There will always be terrible people, doing terrible things. There will always be tyrannical kings, greedy lords, and racist peasants. There will always be pain and suffering, and there will always be injustice. This is not Ciri's burden, it's nobodies burden unless that's what they want. And clearly, through every conversation you have with Ciri, that's exactly the opposite of what she wants.
Ciri might be a good ruler, and maybe in the grand scheme of things she does some good, but is it worth her happiness? Her entire life? I don't think so. Ciri has already saved the world twice, in fact now she's saved every world. She has sacrificed her happiness time and time again for the sake of other people. It's time for her to forge her own way, imo, and not be bound by her blood. It's time for her to choose her own destiny. I don't think this happens if you let Emhyr manipulate her into taking the role as his heir.