Sly Moore is an Umbaran woman who serves as staff aide to Supreme Chancellor Palpatine through the Clone Wars. She appears in Attack of the Clones (2002) — where Sandi Finlay performs her — and again in Revenge of the Sith (2005), in which she is first identified by name.
Present for all of it
She has no dialogue in either film and is in the frame for a remarkable amount of the Republic's collapse: the emergency powers vote, the Chancellor's private conferences, the arrival of the delegation that comes to arrest him. The films never explain who she is or what she knows, and that absence is the character — a functionary whose entire significance is proximity.
Umbarans
Her species is native to Umbara, a sunless world whose people are described in later canon as adept at influencing and reading others, and which becomes a Separatist world during the Clone Wars — the setting for the Umbara arc that introduces Pong Krell. Whether Moore's presence in Palpatine's office is connected to any of that is something the material has left open.
What is and is not established
Legends material went considerably further, making her a Sith adept aware of Palpatine's true identity. That is not current canon, and this entry does not carry it as fact. In canon she is an aide, unexplained, and the encyclopedia would rather record a small verified thing than a large unverified one.