What must a female student do after she lied in a prayer competition, received a gift, and has now repented?

Lying is a major sin that leads to Hellfire, curses, and expulsion from God's mercy. It is one of the characteristics of hypocrites. What the questioner did is cheating and deception, both of which are forbidden. She must repent sincerely, and part of her complete repentance is to return the gift to its rightful owner or to the organizing body of the competition.