Little Lottie is a little brat. Sorry, but it's true. We learn that she has been treated like "a very spoiled pet monkey" and that she is "a very appalling little creature." It's not her fault or anything, but it still makes her unlovable.
Trust Sara to find the good in everyone. They initially share a connection because they've both lost their mothers, but they ultimately become like family to each other—with Sara acting as the mother figure. Sara even makes it official: "I will be your mamma," she said. "We will play that you are my little girl. And Emily shall be your sister" (4.51).
Just like with Becky and Ermengarde, Sara's instincts are good. When Sara suddenly becomes poor, Lottie loves her just as much as ever. Even though she's just a tiny little girl, she sneaks all the way up to Sara's attic to visit her, even after Sara refuses to tell her where she lives: "Lottie was a determined little person. If Sara would not tell her where she lived, she would find out in some other way" (9.10).
And we say—good for Lottie. She can be our adoptive daughter any day.