Here's a picture of Nelly with her Ma.
Whenever I think about Nelly and her life on the farm, I can never seem to imagine Nelly's mother in any scene or situation; things seem to work out pretty well when it's just her and her father.
It's kinda like asking the question "Where's Andy's dad in Toy Story?"
They're just not there ¯\_(ツ)_/¯