[…] [Lucy] was seized with one of those emotional impulses to which she could never attribute a cause. She only felt that the candle would burn better, the packing go easier, the world be happier, if she could give and receive some human love. The impulse had come before to-day, but never so strongly. She knelt down by her cousin's side and took her in her arms (7.25).
Lucy, being a young, emotional, genuinely good person, feels the irresistibly human need for affection – unfortunately, the only outlet she has for it is Charlotte, who really doesn’t seem like the most huggable person. Lucy’s not sure what motivates her need for love, but we are – duh, it’s human nature!