Police said 30-year-old Christina George-Harvan, of Conway, shot 21-year-old Katelyn "Kaytee" Francis of Fairmont, W.Va., around 10 p.m. in the parking lot of a bar in in New Brighton, about 30 miles north of Pittsburgh.
Their wedding was held earlier in the day.
"We believe all three were arguing over who was going to be the designated driver," New Brighton Police Chief Charles Vanfossan told TV station WTAE.
George-Harvan is being held in the county jail without bond. No attorney was listed on court papers.
"Everybody in the bar noticed that there was something going on with the people, but nobody knew exactly what was happening," witness James Botinovich told TV station KDKA. "The next thing you know we heard someone got shot."
A preliminary hearing is scheduled for May 2.