From Bulbapedia, the community-driven Pokémon encyclopedia.
The Massage Lady lives in Veilstone City, in the house nearest the Gym. The Massage Lady lives with her brother and a Pachirisu. Her boyfriend is the Scarf Guy in Pastoria City, whom she keeps in contact with through mail, which she lets Pokémon deliver. Once a day, she massages the player's Pokémon for free and finds Accessories for dressing up in Pokémon Contests. It is said massages make the massaged Pokémon friendlier.
This is a list of the Accessories that she can find: