She was born in Joplin, Missouri and moved first to Jetmore, Kansas and then Dodge City, Kansas before settling in Claremont, California. She sporadically studied music at Pomona College. Later, she sang at churches around Claremont and, although she said that her singing was just "a hobby", she self-released a small number of records, mainly made up of classical, gospel and children's songs. It was while making one of these records that the arranger Fred Bock heard her. He convinced her to try some more modern songs, and took the resulting recordings around record labels.
Thanks to this, Mrs. Miller was signed to Capitol Records by their A&R man, Lex de Azevedo. Her first LP on that label, ironically titled Mrs. Miller's Greatest Hits appeared in 1966 when she was 59 years old. It was made up entirely of pop songs, and sold more than 250,000 copies in its first three weeks. Will Success Spoil Mrs. Miller followed later the same year, and The Country Soul of Mrs. Miller a year later.
She appeared on the Ed Sullivan, Merv Griffin, Joey Bishop, Mike Douglas and Jack Paar shows, sang for the troops in Vietnam, performed at the Hollywood Bowl and appeared in Roddy McDowall's film, The Cool Ones. However, as with other novelty acts who were popular in the 60s, interest in Mrs. Miller soon waned. She was dropped by Capitol, and in 1968 she released her last album, Mrs. Miller does her Thing on the small Amaret label. She later put out a couple of singles on her own Vibrato Records. By the mid-1970s, she had retired from singing.
Mrs. Miller's success, like that of Florence Foster Jenkins, was undoubtedly due to the perceived awfulness of her singing. It seems that Capitol were keen to emphasise this -- in a 1967 interview with Life magazine, she said that during recording sessions she was conducted half a beat ahead or behind time, and the worst of several different recordings of a song would be included on the finished record. She claimed to be initially unaware that her technical inability was being ridiculed, but eventually realised what was going on. At first she resented this, but eventually decided to play along with the joke. Nontheless, she later attributed her split with Capitol to her wanting to sing "straight" and record ballads, and Capitol wanting to continue with the "so bad it's good" angle.
Mrs. Miller died in Vista, California. In 1999, Wild, Cool & Swingin' , a compilation of her work, was released on Capitol.