All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Whoever has reached the age of fifteen has become a pubescent person, therefore he is considered a man and has the same rights and responsibilities. Therefore, if there is no closer guardian to the woman than him, then he is her first and most suitable guardian - like this Muslim brother in this case - who has priority in marrying her off than someone who has a general mandate, such as a Sharee'ah judge and whoever takes his place. There is no need then to reconduct the marriage contract, nor to involve another Imam and the like.
Allah knows best.