The Davis Sisters
The Davis Sisters,(Wikipedia) Betty Jack Daniels and Mary Frances Penick, were not sisters. Returning home one night from Wheeling, West Virginia, they were struck by a sleeping driver. Daniels was killed, and her funeral at Latonia Baptist was said to be one of the largest ever held in the area.
The death halted a budding career of
the group. They had been booked on Eddy Arnold's TV show, and the
Grand Ole Opry, due to their first big hit, on RCA, I Forget More
than You'll Ever Know.
There's an extended article about them at this site. You can search online for more about them, but be aware there's gospel group from Philadelphia that's also called the Davis Sisters.
Mary Frances Penick continued to sing - you probably know here better as Skeeter Davis(Wikipedia).
Here are three samples of Davis Sisters' cuts from Youtube: