“My instinct tells me, that as an O-3, the chances are fairly good that she is indeed an obligated reserve officer as many physicians will use the Army to pay for medical school, and of course there’s an obligation associated with that.”
I believe a Captain is an O5.
No, O-3, except for Navy and Coast Guard, where they are O-6. Navy O-3 is Lietentent. All the officer grades wear the same insignia though. "Railroad tracks" for O-3, Eagle for O-6 (Colonel/Captain). See this DoD page
O-5 is Lt. Colonel/Commander, with silver oak leaf insignia.
Captain is an O-3 in the Army, Air Force and Marines. Captain is an O-6 in the Navy and Coast Guard.
Navy & Coast Guard, Captain is O-6, elsewhere it’s “our” version of an LT (O-3).
JG, USCG retired