People who are sinning in that way always distance themselves from God. She is having an emotional affair, and is headed for a physical one.She is also lying to you and deceiving you.
You can either challenge her on it and say that you know she is lying, or you can suggest that you go have decided to take time off work to go with her as you need a break, and see what she says, or you can let her go knowing that she will probably have a full affair.
When we are tempted in that way, God tells us to flee. Not to fight it, but flee. She is intending to flee towards this man.Do you honestly think she will go and see him and not do anything?She is walking into the fire.
You need to make a decision what to do before she goes. She also needs to stop any contact with this other man if she wants to save the marriage.
I would not trust her. She is lying about going on a work trip to see another man. Therefore she has shown that she cant be trusted, unless she repents and changes her mind before she goes. How did she meet this guy?.