(Disclaimer -I don't know much about HIPAA laws, so most of this is just me guessing.) Even if HIPAA laws would prevent the hospital from releasing information about her condition, I don't think they could/would refuse to tell her next of kin (her son, I would think) that she was there - unless she is awake and able to tell them not to. But if they had to wait for permission to release that info, no one would ever find out their loved ones were in a hospital after an accident until the patient was awake and communicating - and I know they don't always wait for that. I have heard of some hospitals that won't even connect callers with a patient's room (unless they already have the extension number) because they don't want to confirm that someone is a patient there, but I don't know if that's standard practice everywhere now. Either way, I think they would release that info to her family (or at least the police, in a case when a missing persons report was filed) unless they were directly ordered not to by the patient.
I hope there turns out to be a simple explanation for this and that your friend turns up soon, healthy and safe.