The differences between Louka and Raina are both social and behavioural. On the one had, Raina belongs to the upper class as a daughter of aristocrats. On the other hand, Louka belongs to the lower class and works for the aristocratic Petkoffs as housemaid. Raina, as an aristocrat, tends to look down on Louka as she believes she is superior to her by reason of birth. For instance, she will not want Louka to tell the family what to do when the latter warns them to take cover against the smoking guns.
On her part, Louka does not accept an inferiority status and sees Raina as her equal irrespective of her aristocratic status. And so she does not hesitate to call her by name. Raina begins as an idealist and seems to be enamoured of Major Sergius owing to his so-called chivalry and heroism on the warfront. She does not appear to know what she actually wants in him. Therefore she continues to waste time, day-dream and date both Serguis and Bluntschli at different times. On the contrary, Louka is a realist and a schemer. She knows what she wants in marriage from the outset. Her grand design is to use marriage to climb up the social ladder and join the likes of the Petkoffs at the top. And she deploys everything, including boldness, eaves-dropping, gossip, blackmail, wit and seduction to turn Sergius and Raina against each other and then wins Sergius as would-be-husband. Raina is complacent and believes that her social status is a sufficient credential to make anybody fall in love with her. Louka, on her own part, knows her limitations as an underdog. She never takes things for granted and she always keeps her ears to the ground. That explains why she boldly retorts:
"My love is at stake i I am not ashamed" when Raina accuses her of jealousy and eavedropping.