She spends her days on treetops, looking down on everyone. Jeering at them when they feel joy and happiness. She's envious of their bliss and the fact that yet again she will not be in Santa's good books. So she plots to wreck everyone's holiday, ruin their decorations, unshovel their snow.
But no matter how hard she tries, she never succeeds, it's always one failure after the other. She can't really touch their happiness, she's tried.
So she bares the loneliness all by herself, watching yet again, from the treetops, as the kids run across the streets laughing and smiling at snow angels and the parents decorate their lawns. She sits and watches as everyone has fun, without her.