Erina

Erina is a Pokémon Trainer and a character of the day who appeared in Lost at the Stamp Rally! (BW051).

Erina was first seen searching for her lost Axew in Gear Station. Eventually, she asked Cilan for help as he gathered stamps for the Subway Bosses' Stamp Rally. He accompanied her on her search, and they eventually found a note posted as a clue to Axew's location, which had been left by Iris and Ash. Cilan then asked Emmet and Ingo to help them track down Axew's location. They quickly locate Axew, who was reunited with Erina.

However, with all of the time spent searching for Axew, Cilan had failed to complete his own goal, to collect all of the stamps he needed to battle Ingo and Emmet. Erina allowed him to have her stamp sheet, which had the stamp Cilan required to complete the Stamp Rally. She then watched the battle alongside Iris, and afterwards, the four of them rode the Ferris wheel together.

(Source: Bulbapedia)