But it also fits with her backstory
Plus, putting aside the conventions of serialized TV shows, Maeve's decision also made sense with the rules Nolan and Joy have established throughout the show's run. From Dolores to Bernard to even poor Teddy, each host's personal revelation has been related to a painful Ford-penned backstory, a defining traumatic event that proves unshakable and sends them on the pathway to self-awareness. "Your memories are the first step to consciousness," Bernard told Maeve last night. "How can you learn from your mistakes if you can't remember them?"
On a surface level, it appears that Maeve has not learned from her mistakes: by getting off the train to find her "daughter," she's delaying her own freedom by returning to the brutal, violent prison she's been living in her whole life. She's heading back into danger to rescue a fellow robot who was only programmed to appear as her daughter. The "daughter" is a lie. She makes the sentimental decision, but, as Ford said in his pre-death monologue, there are lies that tell "a deeper truth." By getting off that train, Maeve is effectively buying into the lie -- proving she just might be, as Ford and the robots in Daft Punk would say, human after all.