She's the braindance expert that you'll meet before the end of Act One, as the friend of Evelyn that helps you with the plan to steal the biochip from Arasaka.
Once you've got over the fact that Johnny Silverhand is now part of you, you'll start trying to hunt down a way to get him out of your head again. Part of that main quest will be an attempt to track down Evelyn. Well, it's here that you'll cross paths with Judy again. Make sure to take advantage of any optional objectives you get to call her and keep her involved with the story, as that way you'll start spending more and more time with her.