I think she started expousing in the police station and they sent her to the psych ward as a result.
Well, it could have been smart as a way to avoid prison but once she was in the bin she could have changed her discourse for something a little more... not completely insane. Telling the psychiatrist that thinks she's crazy that he should let her go because her son is in danger is just plain dumb. Plus become violent and stab him with his own pen si even dumber.
We have someone who's smart enough to amass a fortune in weapons (remember the underground cache?) but stupid enough to insist on having the behavior of a violently insane person in an Insane Asylum!!!
You get the point?