My feeling on this is that I wouldn't be ok with someone dictating who I could see while they were free to see whoever they happened to be attracted to. At the moment I have no interest in other men but if it did come up and I did become interested in a man I know that my husband and I could work through it. For me it's a matter of respect and equality.
You have every right to be uncomfortable with her being with another man but it also your responsibility to work out why you are uncomfortable with it. If she doesn't want to be with other men at the moment that's great it means that you have time to work through it and find the why before she does develop an attraction to another man.
Everything will be ok in the end. If it's not ok it's not the end.