People only seem to remember the bad with Lori, when in reality she's the responsible voice of reason and leader of the siblings. Her only super mean point was in the Driving Lesson episode, and even then, the end of the episode had her going out of her way to fix the damage she had done by actually being a good sister and teaching Leni to drive.
Hell, there was even an episode that showed that the only reason Lori is bossy and strict is because the rest of them are fucking animals who destroy everything they touch. If they calm the fuck down, she's down to have fun too. All she asks for really is a bit of respect from the others. That's all.
tl;dr If you were to put Lori on a scale of who is the meanest/bossiest sibling, she would actually be somewhere in the middle with Lincoln and Luna.