After I heard the flawless song that Rih rejected, Go, I decided to give her a listen.

What songs should I focus in on? What's her best?

Oblivion or Genesis are good places to start, but my personal fav is Symphonia IX. Not going to lie, don't go into it expecting songs that sound like Go

the only Grimes song I have is Circumambient

None of her songs are really like Go. Listen to Phone Sex, her collab with Blood Diamonds (the cowriter and coproducer of Go). He has a more hype sound, Grimes is more experimental.