This is Andy. She is the love interest of Brand and best friend of Steph. The girls joined the adventure when they stopped to check on Brand after is run in with the local jerk and son of the people developing the country club
The Goonies, a group of friends living in the "Goon Docks" neighborhood of Astoria, Oregon, face foreclosure on their families' homes from the expanding Astoria Country Club. On one of their last days their morale sinks particularly low due to Mikey's older brother Brandon having failed his driver's license exam, thwarting their plans to "cruise the coast in style" during their "last Goonies weekend." While rummaging through the Walshes' attic, they find an old newspaper clipping, a Spanish map, and an artifact relating to a rumor of a lost but not forgotten pirate treasure somewhere in the area. Hearing the call of adventure, Mikey tries to persuade his friends to join him in search for the treasure hoarded by a pirate named One-Eyed Willie. Initially reluctant, the group eventually decides to evade the authority of Brandon, and escape for one last "Goonie adventure."