When Camacho was dismissed from Kenny Rogers and The First Edition, Arnold took her spot in the band, beating out Karen Carpenter for the role.[3] She stayed with the band until it disbanded in 1976.
After the two were introduced by Rogers, Arnold married singer Roger Miller.[4] After The First Edition disbanded, Mary toured and recorded with Roger until his death in 1992.[3] After his death, Mary became president of Roger's musical trust. In 2004, she sued Sony/ATV Music Publishing to regain the rights to Roger's music. She won in district court in 2010, gaining the rights and $900,000 in damages.[5] However, the verdict was overturned upon appeal, and Sony retained the rights to Roger Miller's catalogue.[6][7]
Arnold also performed with Waylon Jennings, Glen Campbell, and George Burns. She performed at the White House twice, before the Nixons with The First Edition and before the Fords with Roger Miller. She was inducted into the Iowa Rock 'n' Roll Hall of Fame in 2009.[3] She last appeared with The First Edition at a 2015 panel at the Country Music Hall of Fame and Museum.[4]