I can understand your dilemma; no one wants to be around someone who's constantly complaining or making critical comments. The Bible says an undisciplined tongue "is a fire, a world of evil among the parts of the body. It corrupts the whole body" (James 3:6).
At the same time, I hope you'll seriously consider including your aunt in your Christmas celebration again this year. Elsewhere, you mention that she's alone and you seldom see her; refusing to invite her will only add to her feelings of isolation and bitterness. (In fact, I can't help but wonder if her situation has contributed to her negative attitude toward others.)
What can you do to keep her from spoiling your time together? First, pray for her, that God will not only convict her of her critical spirit, but will help her turn from it and have instead a spirit of thankfulness and peace. Pray, too, for your attitude if your aunt does come, asking God to give you a genuine spirit of love and concern for her. And if He opens the door and it seems helpful, quietly encourage her to be more positive in her comments. Our words can have surprising power; as the Bible says, "a gentle tongue can break a bone" (Proverbs 25:15).
Then think through your time together. For example, think of ways your aunt could be kept busy, instead of simply sitting around talking. Most of all, make Christ the center of your time together. Complaining flees in Christ's presence.