It is vital to realize that this poem explores the mixed feelings of the speaker and her father at having arrived in America. Although they have left a place of danger and insecurity behind them, they feel overwhelmed by the vast differences between their new home and their old. The speaker says how they desperately were "trying hard to feel luckier / than we felt."
It can be both, because the definition of blithe is “showing a casual and cheerful indifference considered to be callous or improper.” And that is negative, but the other definition is “happy or joyous.” Which is positive
