They were in IFR conditions. It’s very easy to become disoriented and lose spatial awareness. My guess is that the crew stalled the aircraft, didn’t believe they were in a stall and entered an accelerated spin. Hopefully they’ll be able to get some recoverable data and actually determine if the cause was pilot error or if the aircraft broke up mid-air.
However, that does not make this tragic outcome any less tragic. That patient and her mom should have been safely flown home and the family should have been celebrating her recovery after successful treatment at the hospital she was just discharged from.