She’s “Catholic,” as most of the Kennedys are, but even so, annulment would be relevant only if she wanted to remarry in the Church. Assuming she wasn’t complicit in the scam all along, maybe she’d be happy single, with her children and her other pursuits.
The Church encourages reconciliation between spouses, but the wife of a serial adulterer isn’t held accountable for not staying with him forever, especially if he dumps her.
I can’t imagine being married to a celebrity. It would be a nightmare.