BEWARE OF BOOK SPOILERS (but honestly, that can't be avoided in a spoiler discussion about the storytelling, and much of it got revealed during TW2 anyway, at least CDPR's interpretation of it):
Wow, wait. The end of the books can be interpreted in many ways. We don't even know if Geralt or Yen were really saved. And we don't know if Ciri got back any powers for good. We know that Ihuarraquax enabled her to do something with Geralt, maybe saving him. But she had to touch his horn while doing so, so in my interpretation it's the unicorn's powers Ciri is chanelling here, not her own ones. But I agree that you could interpret that in other ways as well.
After all, the end is pretty much open. In the last passage of the book we learn that it was actually Ciri's tale. She told Galahad about the events in Rivia and about Geralt's and Yen's supposed. We can only speculate how much of that tale is actually true or not or just the ending Ciri wished to be. Galahad noticed that she cried while telling him the story so it's quite possible that the ending isn't all that happy. I'd say at least the passage on the isle in which Geralt and Yennefer talk (the 2nd last passage of the book) is more of a fairy tale than the truth. And then again we have to ask ourselves why Ciri had to drive them away in the boat if she just had regained the powers to heal them.
I think there is much to debate and discuss about the ending of The Lady of the Lake and making solid statements is a bit hard here. That's actually one of the reasons why I love this open but still conclusive end so much - it gives you space to interpret and to adapt it to your liking.