My understanding is that in Noonan’s puberty can be delayed in boys, but is it the same for girls? My fifteen-and-a-half year old girl is a physically fully developed young woman but hasn’t had her period yet. She is PTPN11 with a pulmonary valve stenosis.
I don’t think we recognise progressive liver disease as a common association with Noonan Syndrome. If there’s no sign of any auto-immune issues then I think the liver team should treat you as they would anybody presenting to the liver clinic. They like to do lots of tests and that would seem to be the sensible approach in this case.