Hmm, I dont know, I never found a problem with her detachment being part of the brother/sister relationship. As Grandma Longneck hints, she did take Pterano's being kicked out hard even if she didn't stop it since, how could she if he was truly in the wrong and Grandpa Longenck and the others in the right.
Plus it's not like she could just tag along to check up on Pterano since she has her whole brood to look after.
I always just got the impression she was probably older and very very disappointed in where Pterano's life was heading. Secretly hoping he would change, but not naive about such like Petrie and realizing how it would take a big jolt (such as he seems to get after the Ducky incident) to cause such.
Again though just spewing my thoughts.