Christina Bond, mother of two, was a local politician and also a pageant champion.
"She was having trouble adjusting her bra holster, couldn't get it to fit the way she wanted it to. She was looking down at it and accidentally discharged the weapon," St Joseph public safety director Mark Clapp was quoted as saying by The New York Post.
She was rushed from her home on Lake Michigan after the incident, but succumbed to her injuries at a local hospital.
She also won the 2013 Miss Michigan Figure Overall body-building championship.
Gun accessories such as bra and purse holsters, designed for women, have grown in popularity over the last few years. Many businesses now cater specifically to female gun owners.