You are right to see a difficult class struggle in the character of Louka! She absolutely hates her station as a maid and a servant. Why? Well, first off, she is interested in Major Sergius Saranoff (and he is interested in her, too) even though she is engaged to another servant, Nicola, at first.
In fact, Nicola nicely serves as Louka's foil (at least at the beginning). He is always talking about how people should live according to their station. In fact, Louka disagrees completely. Nicola finally sides with Louka when he sees that her marriage to Saranoff could be beneficial to both of them.
Soldiering, my dear madam, is the coward's art of attacking mercilessly when you are strong, and keeping out of harm's way when you are weak. That is the whole secret of successful fighting. Get your enemy at a disadvantage; and never, on any account, fight him on equal terms.
Evenutally, a duel is proposed and Sergius' Raina questions why the two are going to fight. It is then that Raina knows that Sergius truly has eyes for Louka. Finally rising above her station, Louka and Sergius do become engaged!