In Act II, Catherine asks Raina, "Will anything ever make you straightforward?" Is there an earlier instance in Act II when Catherine finds Raina...

There are two prior moments in Act II when Catherine appears to be disapproving of Raina for doing something that isn't "straightforward" (frank, unstudied, simple, or honest). The first occurs when Raina makes her splashy entrance. Sergius asks Catherine and Petkoff about Raina ("How is Raina; and where is Raina?") and Raina immediately responds, emerging on cue:

RAINA [suddenly coming round the corner of the house and standing at the top of the steps in the path] Raina is here. [She makes a charming picture as they turn to look at her. She wears an underdress of pale green silk, draped with an overdress of thin ecru canvas embroidered with gold. On her head she wears a pretty Phrygian cap of gold tinsel. Sergius, with an exclamation of pleasure, goes impulsively to meet her. She stretches out her hand: he drops chivalrously on one knee and kisses it].

The naïve observer might think this is lucky timing, or the result of some superior social sense on Raina's part. Her own father seems to be of that opinion. But Catherine knows better. Her daughter doesn't just enter a room because there are people to meet. She hides out of sight and listens so she can enter when it will have the most dramatic impact:

PETKOFF [aside to Catherine, beaming with parental pride] Pretty, isn't it? She always appears at the right moment.

CATHERINE [impatiently] Yes: she listens for it. It is an abominable habit.

Next, Raina is less than straightforward again when she questions her father about the mysterious Swiss man.

Raina is pretending this is just idle curiosity, when in fact she is keeping a secret, and trying to determine if her father's Swiss man is also her own "chocolate cream soldier." In this case, Catherine either

(1) thinks the questioning has gone too far and wants to hint to Raina to stop, or

(2) she thinks the question is a good one to ask, but feels the need to act reproachful in order to allay suspicions and help conceal the reason for Raina's curiosity.

RAINA. What was he like?

CATHERINE. Oh, Raina, what a silly question!

Either way, this scene furnishes more evidence that Catherine is being hypocritical to despair over her daughter's lack of straightforwardness. Catherine has been part of the "chocolate cream soldier" deception from the beginning, and she, like Raina, is play-acting now. And as we see later with the business of the coat, she deceives with the skill of someone well-practiced in these sort of farcical social maneuverings. Catherine knows how to bluff and persuade with a grand, authoritative air. Raina takes after her mother.