Following her silver medal at the European Athletics Junior Championships in 2003, Cuddihy moved into senior competition. At the 2003 World Championships in Athletics held in Paris, France, Cuddihy qualified for the final of the 400 metres with a time of 53.68 seconds. She participated in the 2004 Irish National Indoor Championships in Belfast, Northern Ireland, where she won the 400 metres in a new all-comers record of 53.50 seconds over Moushaumi Robinson. As a result of her win, she was automatically selected to be part of the Irish team for the 2004 IAAF World Indoor Championships held the following month. At the championships, Cuddihy finished sixth in her heat of the 400 metres, failing to progress further. She was also part of the 4 x 400 metres relay time with Michelle Carey, Karen Shinkins, and Ciara Sheehy. In July 2004, Cuddihy came second in the Irish National Championships behind Shinkins. In July 2005, Cuddihy finished second at the Irish National Championships behind Shinkins. At the 2005 World University Games, Cuddihy made it to the semi-finals of the 400 metres, but failed to progress further after finishing fifth.