Lissa.
Lissa is based on just such an old friend of ours.
And she was much like this, a traveller who comes and goes. And some day, she will return to Walter's life. And that will be really interesting to watch. (Actually, she was slated to appear in the first new story after the original mini-comics run finished at issue 25. But when those plans were scrapped, the story was put on hold. But someday...)