1999 Oldsmobile 88 Car is Completely Dead

Car was working normally for 2-3 trips. While driving at about 10mph, the car suddenly died. Engine turned off and all electrical stopped working (no lights, no power windows, no dash lights, no idiot lights, no engine, etc.). Coasted to a stop.

Tried jumping and while jumper cables attached still no dome lights, no interior lights, no dash lights (when key in run position), no power windows. Completely dead.

Main Fuse? Ignition switch? Completely shorted battery? Any suggestions?

I'm trying to diagnose this problem on my daughter's car located 200 miles from me so this is second hand information.