She was originally hired to replace Reba as a receptionist in Brock's office, right? But later in the show they say she's a dental hygentist which Reba is not.

Is that a hole in the plot, or ......

Well there are alot of errors in her work at Brock's office. First they say Brock hired her as the dental hygienist 10 months after he and Reba separated in season one. Then in season two she was teaching Reba how to do the receptionist job, it's possible she was doing that because they were short handed. But then in season three we learn that Reba hired Barbra Jean to replace her even though in that season two episode just mentioned Reba had never worked for Brock before. Then in season five when being audited by the IRS Agent Miller says Reba worked for Brock in 1998. So there are many inconsistencies on what BJ and Reba did at the dental office.