Leni is strict but obviously has a limit to it. Here domineering tendancies are merely a symptom of how much she cares for the people in her lives. Being the eldest child, she is often seen and expected to be a tertiary parent of sorts. Combine that with having to handle 10 other bombastic personalities, it's basically required to police her siblings with equal force. It keeps not only herself, but everyone out of trouble with their parents.
However, she isn't some sort of ice-queen, she genuinely enjoys her time with everyone. Her sisters and brother come to her for good reason. They know that she's reliable enough to come to for just about any issue.
Her relationship with Bobby is sort of similar, in that he needs a constant maternal figure to care for him. Though most of her doting is due to infatuation for him. He's a compassionate, and very hard working guy, but also like a grown up toddler.
You made me go on a tirade about a children's cartoon character.