According to the wiki and Umineko (dubiously canon compliant in Higurashi, to be sure), Hanyuu did actually know Takano was the culprit behind Rika's murders, but kept quiet on it because she didn't want to lose Rika. It does seem a little suspicious that, as the deity for all of Hinamizawa, Hanyuu wouldn't know who was behind it all, but then again, neither the manga or the anime confirm she does anything more than linger around like a ghost with occasional telekinetic powers.
See you guys again next June!
June 30th, 2020
Numinous means faith
Faith in the presence of god
This Hanyuu protects
Why she is silent
Why the culprit is unknown
In Hanyuu's own place
This is why she dies
Over and over again
Stay at Hanyuu's side
Don't learn and leave
Rika must stay and see here
To solve is to leave
A goddess alone
Throughout all time, isolated
But not now with her
A logic error
Unsolved mystery a lock
Keeping Rika in
Why she is silent
Why the culprit is unknown
In Hanyuu's own place
11.06 PM, USA Central Time