She might have lost a child in the past - I haven't seen the movie with Sue in it for a long while. Another thing (somewhat) like this is in LBT 3, during Mr. Threehorn's song, and he said "When the trail gets rough, you gotta get rougher, to help your family survive," and we pretty much know that Cera's mother and siblings were...pretty much never seen after the first movie. I think someone posted pictures from LBT3, when Littlefoot and the gang were stuck in the quicksand. Uh...pictures of another threehorn in the background of Topsy who reacted with fear when they heard Cera's screaming who may and probably wasn't Cera's mother.
Wow. I hope that made sense. It's somewhat similiar, in any case...