America loves her family—no one can debate that—but the girl has a very different relationship with each of her parents. Her relationship with her mother is sometimes contentious, while her relationship with her dad is all love, all the time. That's a striking contrast. What's more, these contrasting parental units are part of what makes America such a compelling personality.
America's relationship with her mom gets a little hairy at times. Mostly, this is due to the pressure Mama Singer places on America: America is the oldest child in the house and as a result, she has to take on the most responsibility. In addition, many of the conflicts between America and her mom are rooted in their similarly strong-willed natures. Check out this passage, for example:
She couldn't stand when I was stubborn. But I got that from her, so she shouldn't have been surprised. (1.8)
In other words, America's relationship with her mom is a classic case of an unstoppable force meeting an immovable object. Although it's obvious to us as readers that America's mom loves her a lot, America sometimes can't see past these conflicts to see her mother's affection.
In contrast, America's relationship with her dad is all sunshine and puppies. Mr. Singer clearly adores his daughter and approaches her with a much softer touch than his wife. We can see this most prominently in his reaction to the Selection: unlike Mrs. Singer, Mr. Singer places zero pressure on America to enter the competition.
We can also see the difference between Mom and Dad in America's feelings towards her pops when she ships off for the palace: "It was too much to bear, to be loved that much. I'd be surrounded by scores of guards at the palace, but I couldn't imagine a place safer than my father's arms" (7.46).
Despite this contrast, however, it's clear that both of America's parents have played a big role in making her the woman she is today. She wouldn't be tough and resilient without her pugnacious mother; she wouldn't be kind and compassionate without her sensitive father. Even if they drive her crazy sometimes, Mr. and Mrs. Singer are largely responsible for America's wonderful yin-yang of a personality.