In the 7th episode of The Witcher Tissaia de Vries meets Yennefer in Aretuza and says:
You ruined one life. Stop there.
Whose life did Tissaia refer to?
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Yennefer's own life, because she chooses to stubbornly undervalue it.
Tissaia and Yennefer have (had) extensive dialogues about the worth of the latter's life, about her fatalism, existential doubts, and, most of all, her 'legacy' - these are the traits that make her character memorable, in which she sees her weakness, but Tissaia her power.
In Episode 2, during the forming years of Yennefer, Tissaia continuously appeals to her self-hate to unleash the raw power or chaos within her:
T: "You take weeks to lift your stone. You can't bend water. You struggle to perform the simplest physical tasks. And now you lie to me? Your worst fear makes such sense.
Even if you were a beauty, still, no one would love you."
While Yennefer sees it purely as weakness:
Y: "You should've let me die. At least I had control over that."
T: "Oh, that's adorable, piglet. You weren't taking control. You were losing it."
During this first lesson (or trial), the flower, there to provide the energy necessary for magically elevating the stone, serves both as a symbol of life that must wither in order to create anew, and of Yennefer's character - all beauty must die.
Even though her ensuing beauty fools others, it is a fabrication, another illusion, paid for with too large a sacrifice, unable to soothe her ugly self-image.
She's implying Yennefer has ruined her own life. This is pretty clear from the context, but it's made more explicit in the next few lines of dialogue:
Tissaia: You ruined one life. Stop there.
Yen: I never even wanted to come back here!
Tissaia: Then you failed at that, too.
Yen: You say I never took responsibility for the way my life turned out. What about you?
This is again emphasized in the next episode:
Triss: So, are you ready?
Yen: To die? Yes. I've lived two or three lifetimes already.
Triss: But you haven't been satisfied in any of them.
Yen: I've tried. But I've no legacy to leave behind. No family. It's time to accept that life has no more to give.