Recognizing where the responsibility (blame) lies is necessary to correct the situation.
I don't find it necessary, but I understand some people feel this is needed.
She believes that she alone is responsible and it's up to her alone to make their marriage work. WRONG!
If that is what she is doing, then I'd agree it's the wrong way to go about it.
While she may be a contributing factor to her deteriorated marriage, prompting her husband to take up with her best friend, It was her husband, not her, who sought to correct the situation by taking up with another woman. He could have chosen otherwise. She was blindsided and had no choice in the matter.
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I don't think the point was about what could have been done different in the past but to correct the current situation moving forward.