@Elrinion
She becomes a self-sabotaging ruler, not retarded. Retarded implies she's too dumb to realize what she's doing as dumb, but she doesn't even have that idea, vehemently believing her ideas to be the best.
And well, considering she was trained as a knight previously, she didn't really get any training about subterfuge or actual plotting, so she's essentially a 'My cause is righteous!' meathead.