I think we've chatted about the overbite before. Not good, but not quality of life threatening and often they give a look of "character" to a puppy/adult.
Chip definitely has it great.
IF you do decide to go back to Chip's breeder for a little sister, then maybe you can ask her to incorporate some of the "Rules of Seven" suggestions with "lil sis" before you make the ride home with her. Be a lot less stressful on both you and baby girl. And breeders often will work with homes (especially a repeat buyer) to help things go easier.
Debbie