Your feelings are completely valid. it’s normal to feel uncomfortable about her meeting an ex. She showed respect by asking you first, which is good.
What to do: Tell her how you feel calmly not “don’t go,” but “I feel uneasy because of your past with him.” Ask for transparency or invite yourself if it helps you feel safe.
Watch her reaction: If she respects your feelings, all is well. If she dismisses them, that’s the real issue.It’s about honest boundaries, not control.