As an extension of what Perna commented on - and I'm not so certain if this was addressed, as my focus these days is nil - have you shown her the results of this questionnaire? Perhaps that might open her eyes even more.

And as an outsider looking in, I don't believe people that have affairs - emotional or otherwise - do so all the time out of malice or hatred or spite for their partners. In fact, it angers me when people immediately point the finger and call the person "evil", but it's never an easy call to make. Depression can make a person do things that they'd never ever predicted they'd do. Whether or not you both see a counsellor together, I truly believe that your wife needs one on her own. Depression - and other mental issues - can bring a person so low that they might do just about anything to grasp for a spark of hope.