Should I be jealous or worried that she had this long conversation with her ex and did not tell me about it? I would never think of having a talk like that with my ex and not telling my GF. It seems to be lying by omission in a relationship where we agreed there would be no secrets.
Should I confront her? Suggestions on how to broach this?
Me neither. Nor would any other fully-recovered and back-to-health thus ready-to-re-marry individual. So there's your answer.
A healthy would have told the ex it was too late and that his clandestine attempt to lure her back were wholly inappropriate and unacceptable considering the healthy'un's current position and status, "thank-you and goodnight - CLICK, BRRRRR...". Failing that, the healthy'un would at the very next available opportunity approach to inform YOU that their ex had called them while 'your back was turned'.
What would you think if you told me, your new partner, that you had a phobia about spiders and then the very next day, found a tarantula lurking in your shared sock drawer? Mere accident? Pff... yeah, right.
Red Flags, Red Flags, Red Flags, all over the shop. She is not remotely fit to be someone's relationship partner, let alone new wife. And a once-cheated-on, KNOWING FIRST-HAND how painful all those untowardnesses and flags are, knowing how especially painful to an already betrayed, would avoid all such activities like the plague, would rather stick pins in their eyes than behaviourally associate themselves with a relationship monster. She, on the other hand, whether unknowingly or not, has already subjected you to cheating behaviour (the only person in the world she should discuss such matters of the heart with, is you).
When she no longer cares why they broke up and cannot be a*sed to have a conversation about it *with anyone* (usually after 2 years from the Decree Absolut) is when she'll be fit for a relationship.
doesn't seem you are ready for marriage being so critical of her intentions with another man
Have both of you objectively examine the reasons for the previous infidelity on the part of your spouses? How long have the two of you been cohabitating? To what degree have the two of you committed to each other beyond the marriage certificate which didn’t work previously? Who is the source of your total supply? Why? Who is her source? Why? Can you trust the information shared from these questions?
Whereas there is no guarantee in any relationship, knowing the other’s soul will go a long way in determining if the above issue is a concern in this marriage or not. Please let us know what happens next.