In the books Yen is blinded during the Battle of Sodden because she takes a spell to the face. Similarly Triss takes a fireball to the tits which is why she stops wearing low cut tops but that didn't stop CDPR still giving her an alt dress which completely ignored this.

This blindness is used as a mechanism to explore Yen being unable to use her powers because she can't fucking see and didn't learn the pre-requisite spells needed to see with magic yet.

Also in the books Ciri starts to learn magic. From Yen. She is told there are many things that can be drawn upon to use as a source and that Fire is one of the most dangerous things to do this with so should be avoided.

Ciri does the thing.

And effectively loses her magic capability because of it.

Well the writers gave all of that to Yen and made her lose her magic instead of just her eyesight after the Battle of Sodden. They also gave her Triss' arc from the battle, because the showrunner really just wants to write a self-insert.

Now Yen differs significantly from the book version in multiple ways which go all the way back to how she gets her magic in the show; by literally getting a hysterectomy done via magic. This doesn't happen in the books. This never happens in the books, it's not how magic works. Some magic users end up becoming sterile due to years or magical alterations done to themselves but they don't flat out castrate themselves to suddenly grant themselves magic powers.

So, with that in mind Yen then decides that after making the informed choice to give up her ability to have children, not that she was likely to anyway because she was literally a hunchback prior to all this, she claims her ability to have children was "taken from her". Which is the normal sort of bullshit you can expect from Twitter tier writers since again as mentioned the decision to go through with this was both Yen's and one she was completely informed about. She knew what the cost was.

So after Yen then loses her magic she goes full on psycho trying to get it back. At one point near the end of the second season this involves making a pact with a brand new demon added just to the show where Yen will give the demon Ciri and the demon will give Yen her powers back. Supposedly.

Anyone who has read the books will know how much Yen loves Ciri as if she was her actual blood daughter, and yet the showrunners for the Netflix adaptation wrote in Yen wanting to sacrifice Ciri to a demon because she had regrets about giving up her womb for magic decades ago.

As for Vesemir he learns Ciri's blood can be used to make more Witchers so thinks the smart thing to do is kill her and take the blood...

Entire show is a fucking joke.