Awww...I think Hallee is the cutest name for your pup because you are getting her on Halloween.
You could also spell it as Hallie, or how I think it's pronounced...Holly-but then that should be for Christmas. I do think the way you spelled Hallee is the cutest spelling because it's similar to the spelling of Halloween. Another Halloween name idea...Casper. Hey, maybe Chewie or Chewey (for chewing candy--okay that's kinda cheesey for a meaning, but it is a cute name for a Yorkie because they look like a little Chewbaca from Star Wars)! Wow...I think I need some sleep!
F.Y.I. My favorite girl name if I ever get a girl dog is Sadie.