Do we write it is Red's perspective or as if we are watching it from outside.
So for example would it be
Leaf turned towards Red in astonishment
Leaf turned towards me in astonishment?
Soundwave is right in his response above.
Another angle to look at this is that we're dealing with a visual novel. Everything that the RL player sees is already laid out in front of them. In a situation like "Leaf turning toward..." the RL player will already see Leaf facing them. There's no reason to state otherwise other than from a storytelling perspective, in which case—as you should know from playing the VN—is from the player character's point of view.
You can, however, include notes in between dialogue lines, such as:
Leaf is visibly angry
The purpose of these descriptors is to direct how the character art should be represented during this scene.
On this note, you should avoid lines that follow these expression changes like: "RED:
Leaf looks mad." Of course she looks mad! As a player reading/looking at the screen, it's obvious she's mad. There's no need to state the obvious unless you expand the line into an extended monologue to clarify thoughts that the player will otherwise be unaware of (which should also be used in moderation to keep things moving smoothly).
Additionally on the subject of displayables on the screen, you should be extremely careful not to include elements that complicate how a VN is displayed. This isn't some AAA high-particle CG game. Keep it simple, straightforward, and easy to understand.