The horse she was riding was also killed in the strike and a 15-year-old female relative of Miller's was injured.
The Douglas County Sheriff's Office tells 9NEWS a 37-year-old woman was killed around 3:30 p.m.
Officials responded to 7014 W Rainbow Creek Road in Sedalia after receiving for reports that two people had been struck by lightning.
A woman and her horse were killed Sunday after lightning struck them in Sedalia, Colorado, while a girl riding horseback alongside the woman was injured.
A lightning bolt struck this oak tree and killed a 37-year-old woman and her horse who were nearby.
"Our thoughts and prayers are with the family of the deceased during this very hard time", the Douglas County Sheriff's Office said in a news release. Her condition has since improved, but DougCo authorities could not provide more details about her injuries.
The lightning was part of a fast-moving thunderstorm that swept across the metro area on Sunday afternoon. This was the first lightning-related death of 2017.
If you hear thunder, lightning created it, so find shelter.