The end of Station 19’s third season left many questions lingering, one of them being the question of what happened to andy's dad. The mystery was solved in the most heartbreaking way possible when Andy's mother Elena Herrera (Jaina Lee Ortiz) made a reappearance, which rocked her daughter to her core. It turns out that her father had been a firefighter who died during the Sept. 11 attacks, and she was never able to get over it.
The story goes that Andy’s dad, also named Andy, survived polio as a kid, but suffered from Post-Polio Syndrome years later and ultimately passed away from it. He had been a great dad who gave his children Woody, Slinky, and Mr. Potato Head before he passed, and Andy was left with a lot of memories of him that she had been keeping secret for so long.
This explains why she doesn’t have any pictures of her husband around the house, why she has a little sister that isn’t hers, and why she doesn’t wear her wedding ring when she works at the station. It also explains why her relationship with her son is so important, as it’s a reminder of the father that she missed out on.
While Pixar, like Disney before them, has a tendency to eliminate one of a child's parents from the picture (hi, Lion King), it is still a shame that this one family dynamic is left unexplained. Hopefully, we’ll get to see the truth behind it all in future episodes of the show.