Melissa is Archie's cousin on his mother's side. She used to visit his family from Italy every chance she got. Melissa loved playing with Archie, especially since his reactions and independence was humorous.
She's British but she was raised in Italy with her father. They lived in the countryside and owned horses and a farm. Melissa was happy with her home and her family until she was attacked by a monster. Her father had immediately taken her to Camp Half-Blood but she still came back to look after Archie.
It was then after Archie found out who he was that Melissa became unhappy so she left a couple months after him, to Camp. She hung out with her siblings and sometimes with Archie. Her attraction towards Rowan began when Archie introduced her to him. Nothing happened at first until she knew him a little more and they started dating.