Remember that she is smart and although that surprises you, in fact it should not surprise you at all.
See, her intelligence is the reason she's been able to keep up her facade, her charade for all these years. She is smart enough to trick herself into denying the truth and accepting fantasy as reality.
The mind of an addict is very cunning indeed. I don't quite know what your W's addiction is, but I know my XW is an addict in a few ways and she uses her intellect to protect her from the truth.
