As it seems many people have observed, there is a glitch where a girl will keep you from leaving New Bark Town, despite having a Pokemon.  I found I was able to avoid it in a new game by attempting to leave the town without receiving a Pokemon.  She stopped me like she was supposed to.  Then, I went to the lab and obtained my Pokemon.  After that, I was able to leave the town.  I didn't have to go back to my character's mother or even talk to anyone to leave.

From a programming standpoint, I think what happened was there was some sort of event or something that triggers the first time you try to walk past her, regardless of whether or not you've gotten your first Pokemon.  She then won't stop playing that out until you receive your Pokemon from the lab, which serves to turn that event-thing off.  However, is impossible to get your Pokemon if you've already done so.  It's just something to think about, for those who are doing their own hacks.