But it was never established that she even had any kids.The Madman said:The thing with her kid though was probably just to explain what they worried might become a plot hole.
You see, I always figured the crew of the Nostromo where just a gang of lone truckers who had no real family ties. This being because it wouldn't be very adquate to have a family on Earth when you're hundreds of lightyears in space.
Also, the scene is supposed to emotional or whatever, but we as the audience have never ever met or heard about this kid untill just now. We basically hear that this daughter existed and is now dead all in the space of 10 seconds. So it might else well not even have happend at all.