One problem: Maryland is not a "Shall Issue" CCW state. If she was carrying a gun without a permit, then she was committing a crime. A killing which occurs in the commission of a crime is automatic bad news for the shooter.
I'm going to guess that all parties involved had prior criminal records.
Her second mistake was sticking around to talk to police. She should have took off immediately just like her would be assailants. No good could have come from talking to the police.