Rumors are flying as the Hollywood Reporter speculates that Reba McEntire may be engaging in a tried-and-true method actors use when negotiating pay increases - calling in sick. The industry trade magazine reports that within the past few weeks, Reba's called several times to say she won't be coming to the set of her WB Network sitcom Reba because of a "family emergency." However, Reba returned to the set yesterday. Today, Reba's label publicist confirms that Reba had ''a private family thing'' but says everyone's OK. ''She doesn't want anyone to worry,'' the publicist added. Official spokespeople for 20th Century Fox TV and the WB declined to comment.