It would make sense to me if she did at least suspect an affair, and I think she definitely discussed taking the girls back to NC with her to live there without her carousing and no-longer-caring husband. She knew something was brewing, I'm convinced of it. We know he was not as smart as he thought he was, so there's no telling what she may have overheard or saw that gave her a good reason to know something was happening with that slimeball.
The DA stated SW was aware of suspicious behaviour.
He spoke of credit card bills, at a North Denver Restaurant, when Shan'ann was in NC.
The DA stated the amounts of these, were far more than one person can consume.