When Duke John died of plague in 1348, Elizabeth became the regent for ten-year-old Louis. Elizabeth's regency lasted from 1348, until her death. Her daughter Constance took over as regent for Louis.
This succession occurred when Duke John died from the plague in 1348, leading to Elizabeth's assumption of guardianship for ten-year-old Louis. She held this position until her own passing, at which point her daughter Constance assumed responsibility for Louis.