Ending (spoilers)

I'm not sure what the other endings are as I've only played the game once, but my ending involved Ciri stepping through the elf's portal to defeat the White Frost. Geralt then returns to Emhyr, who's been defeated by Radovid (annoyingly, I didn't realise that the quest where you can assassinate him was available), and tells Geralt that he never wants to see him again. Geralt then returns to White Orchard where he picks up a sword, which I had engraved with a play on Ciri's name. He then meets her at the inn where the game began and they set off together. The epilogue then said that Geralt and Yen lived happily ever after at a cottage in the mountains, while Ciri made her living as a witcher. Elsewhere, Radovid turned on all other races after purging the sorcerers - such an annoying oversight on my part! Emhyr is assassinated by his own people.

Which ending did you get, OP? Or anyone else?

There are three basic endings for Ciri with a whole bunch of variations for other characters in the game.

There are a few keypoints where decisions that Geralt makes regarding Ciri will either create a positive or a negative aspect for her self-esteem.

When she doubts in her ability to control her powers, if you have a drink with her and tell her it's okay to not be great at everything, she loses confidence in herself. But if you have a snowball fight with her, it lightens her mood, gives her a much needed break and lets her believe that everything will be alright.

Another moment is when she goes to meet with the Lodge of Sorceresses to hear their offer. In the past, they've tried to control her and her powers, had her life all planned out, who she was to marry, etc. Now she's extremely distrustful of them and is afraid of what they may be plotting. If Geralt goes with her, it shakes her confidence to stand up for herself because she has him to fall back on. If she goes in alone, with Geralt's encouragement, it bolsters her and she can refuse their offer with ease and earn their respect.

Yet another moment is when she wishes to visit the grave of the boy who helped her in Lofoten. She's troubled by his death and spiritually is quite shaken. If you refuse to accompany her, she won't go alone and feels betrayed and lost. If you go with her, you help to bury the poor boy and regain his honor amongst his people. She's relieved and at peace with the situation then.

Also, whilst searching through Avallac'h's lab, Ciri, Geralt and Yennefer come across the elf's assistant, an arrogant, spiteful woman who does her best to tear down Ciri's faith in herself by telling all sorts of lies to her. Ciri's gut reaction is to act out, destroy the lab, but hesitates. If Geralt takes that opportunity to begin wrecking it himself, she'll join in and they both ransack the place leaving Ciri satisfied. Even Yen gets in her bit by defacing Avallac'h's portrait hanging on the wall behind her.

Ciri can also be taken to see her father, Emhyr. If Geralt takes her and accepts payment for bringing her there, she will be angry and confused, believing that she was nothing more than a bounty to him. But if he refuses the money, she is filled with pride.

In short, you need to have more positives than negatives in order for Ciri to have the confidence she needs in herself to defeat the White Frost and to survive.

The three endings are:

Ciri will defeat the White Frost but can vanish, presumed dead because she does not return. This will happen if there were more negatives than positives.

Ciri will defeat the White Frost, return but will decide to accept Emhyr's offer and become empress when he steps down from the throne. This will happen if you have more positives than negatives AND took her to see Emhyr, regardless of whether Geralt accepted or rejected the money.

Ciri will defeat the White Frost, return, and decide to become a witcher like Geralt. This happens if Geralt does not take her to see Emhyr and has more positives than negatives.

There is another path to the witcher ending as well. These all assume that Radovid is dead and that Dijkstra is also. But if Radovid or Dijkstra remains alive, one or the other will defeat the Nilfgaardians in battle. Emhyr will be killed by his own people due to the heavy losses and there is no way that Ciri could ever become empress at that point so even if you took her to see him and had more positives than negatives, she winds up being a witcher.

Just beat it. Ciri becomes Emperess of anilfgaard, Geralt and Yen end up together, the north falls to the Nilfgaardian Empire.