She didn't remember until the article dropped.
Partly because she'd began making strides in her project. But, mainly, she'd just...forgotten.
Intellectually, she'd always known Thaddeus Nott was a Death Eater. But she'd spent summers at Theo's, she'd met his father, and since she'd never seen the man act bigoted...
Well, privledge blinds.
Still, for all that she knew Theo had long denounced his father, she also knew none outside of Slytherin would ever believe him.
In the end she does what she can-
Hopefully Bartok helps.
-and anonymously sends her patronus.