We learn in the Loki series that so-called "variants" attract the attention of the Time Variance Authority by acting in a way that threatens a diversion from the "Sacred Timeline".
Sylvie is abducted by the Time Variance Authority while a young child playing with toys.
What could Sylvie possibly have done to cause this intervention by the Time Variance Authority?
Kate Herron, Loki Director, explains more here.
But I think there's something tragic, in the sense that we see her as a little girl and she's playing with her toys, and it doesn't seem like it's a big thing that she's done. So I think that's the really key thing with her is that we don't necessarily know what the exact event was, but it wasn't villainous, and it didn't seem [that way]. I think that's the clear thing, particularly with Episode 4, is that obviously our perspective on the TVA started to shift. For example, it was really important for me showing her going through the same process as Loki but it's like, 'Okay, how do we show that through the eyes of a child that's also innocent?' And we should feel, as an audience, wrongfully there.
I have my own idea of what it is, but I think in my head, it's definitely something innocent and something out of her control. Which kind of plays into the fact that not everyone arrested by the TVA is necessarily like Loki and has stolen a tesseract and created this branch. Sometimes you accidentally do just step onto the wrong leaf and you create this branch. Do those people, where it's accidental, do they deserve to go through this process where ultimately they're deleted by the TVA? Probably not. Or maybe they do, for the better of servicing and protecting the timeline.
One popular theory is that she was starting to want to become a hero like the valkyrie toy she was playing with, and so was a variant.
We don't know.
The show deliberately refuses to reveal the nature of Sylvie's "Nexus event", i.e. the event that caused the timeline to branch, and it's mentioned on a couple of occasions that Sylvie herself doesn't know what she did. In Episode 4, she asks Renslayer what her Nexus event was, but Renslayer claims not to remember.
Considering that Season 1 ends with
the TVA's entire history seemingly being rewritten by Kang the Conqueror, and nobody remembering Loki,
it's unlikely that anyone remembers what Sylvie's Nexus event was, and therefore, it's unlikely we'll ever learn what she did to attract the TVA's attention.
