Ada was one of the robotic guards of a caravan alongside Protectron Hurtz, led by Jackson, her creator. They were travelling to the Commonwealth when they were attacked by the Mechanist's robots. Jackson sent a distress signal which Al heard and traveled to their location. Ada is the only survivor of her caravan.
She has been shown in the Automatron playthrough and Fallout 4 - Stream - Robo Mods and WALL-E; the first livestream featuring Automatron. After Al completed the main quest for Automatron he has instead used other robots made via the Robot Workbench. During the main quest she was modified to have two lasers, black paint and a Robobrain head. Towards the end and beyond she was painted red, given Assaultron legs, and substancially better armor.
She made a cameo appearance in Fallout 4 - FROST - Part 29 where Al contemplates recruiting her after receiving the first Automatron quest. He later recruits her in Fallout 4 - FROST - Part 30 after fixing a bug with the quest. He mostly uses her as cannon fodder and mostly does most of his dirty work. After dying from a molotov cocktail in a fight with a survivor base, Al recruits her yet again and enacts his revenge on the base. He then decides to leave it alone after facing the survivor who killed him.
He goes back to Sanctury Hills via the Underground Railroad and Ada is left behind when he attempts to modify her.