At the very least, if there was no DNA, they could probably match Diamond to skeletal remains by dental comparison. She has distinct dentition.I just googled and it seems there can be various skeletal issues for people with this syndrome, but can vary from person to person. Things like scoliosis, hip dysplasia, and misaligned limbs seem fairly common.
I would hope that the family have their DNA on record to compare if possible remains are ever found, or at least that they would provide DNA if something was found.
I'd still like to learn more about the POI (s) articles have mentioned. Does anyone have more info on that?