This is the 1312th most frequent Korean word.
대회에
"대회에" means "in/at the competition" or "at the contest."
In this sentence, '대회에' indicates the event or competition that she is preparing for her participation.
그녀는 대회에 참가하기 위해 열심히 연습했다.
She practiced hard to participate in the competition.
Here, '대회에' refers to the context of the competition where his role as a judge will take place.
그는 대회에 심사위원으로 초대받았다.
He was invited to the competition as a judge.
In this usage, '대회에' designates the location or event where the action of supporting occurred.