Was Olga really that bad?
I remember as a kid and emphasizing with Helga and disliking Olga, probably because her parents paid attention to her more than they did to Helga. But looking back as an adult, she is really the only one in her family that actually cares about Helga. Yes, she is naive and oblivious to her parents neglecting her, but when she's home she actually pays attention to Helga. You can tell she actually loves her. I like to think that maybe eventually Helga moves out of her parents and moves in with Olga.
A few instances where Olga really showed she cared about Helga:
She said it was important to her that Helga liked her fiancé and she wouldn't had married him without Helga's approval.
She wanted to get closer to her by student teaching in her class. I think her telling the embarrassing story about bedwetting was just an oblivious slip up on her part.