well, one interesting theory I really like is that she was with the herd that Pterano lead to their deaths.
Personally, I think we'd get a more interesting story if Papa Flyer (Petrie's old man) was one of Pterano's followers. Perhaps Papa Flyer got Pterano alerted in time but he died in the process. I had a fanfic on that. It would put Pterano in a tiny bit of a better light the way I did it, showing that Rinkus and Sierra filled his head full of ideas and made him proud and whatnot. Also, it would show that they were all along planning to depose of him at some point, once he'd gotten a lot of leaf eaters to make him their leader.
In my version, Papa Flyer's last words were for Pterano to be a father to Petrie as he couldn't. Pterano was gonna do it, but he got, er, banished.
Eventually, he was in the Great Valley (why the heck was he there, he's supposed to be banished?????) with Rinkus and Sierra, and he heard about the Stone of Cold Fire. In my version, his motivation would be to get power so he wouldn't lose other like last time and so he could overrule Grandpa Longneck and Topps and be a father to Petrie. Pterano would have justified using Petrie and even kidnapping Ducky to achieve these ends.
Anyway, Cera doesn't seem to like "No, don't marry Tria! I don't want a new mother after Mom! It's not right!". But then, again, maybe Cera accepted whatever happened to her mom.
(Perhaps Cera's mom got mad at Topps (hard to blame her if she did!!!!) and left and took most of the kids with her.

)