anon789,
Sorry you're here, I sure when you both said "I Do", this wasn't what you envisioned to be in your married life.
First, what do you want? To Reconcile (R) or Divorce (D)?
Most will tell you, you don't have to choose which way immediately, but your Married Relationship is at a crossroads right now. If she goes on that trip and stays, she will cause more damage to your M, than you may be able to handle. If your WW becomes truly remorseful, then anything is repairable, but not while she is in an active affair.
Don't confuse remorse with regret, on the surface they can look the same. Remorse is more like OMG what have I done, regret is F' me, I got caught.
Right now she thinks you don't know, once you tell her and she continues, well that sometimes puts the Betrayed Spouse (BS) over the edge.
To state, if you want to try to see if you can "snap her out of it", then shock and awe is your best move.
This may be too late but, if she hasn't left; tell her, DON'T GIVE UP YOUR SOURCES OF INFORMATION.
Remain calm, don't raise your voice, cry in front of her, or beg (Pick-Me Dance). This makes you look weak, and will surely push her away. It makes the OM more desirable.
If she is already on the plane, send the email, let her know she can immediately come back and discuss the Affair and her giving a full accounting of her actions or...
She can go to her parents house to pickup her things, as you will be filing for D (you don't have to complete a D, but having her served is another shock & awe measure. Don't threaten her with D, she has to see it on paper, when she is served. Threats are weak, you have to state actions and carry then out, otherwise she won't take you seriously.
She has to see consequences for her actions.
Before you do anything rash, as in:
Changing the locks on the house.
Destroying personal affects.
Cutting off finances that can leave her stranded in a foreign country.
Talk to a lawyer first. Vindictive actions can hurt you in a Divorce case.
If you have contact for the OM, you could try talking to him. Not all OM/OW are POS's, he may believe he's dating a single women. Finding out she's married with kids may make him back off. Just don't count on it; it depends on if he has a moral code.
The more actions that you take that are strong and decisive, the better you appear.
On the opposite side for your WW (Wayward Wife), don't take her word right now for anything without seeing actions that directly back it up.. Right now her words don't mean anything, such as:
I'm staying in NZ, but I won't see him. LIE
We haven't had Sex. Most likely not True.
If she says she wants to save her marriage, she will need to write a timeline that covers the A, including who supported or helped her.
You will need to polygraph her. This one is big; you can't rebuild a M, without proof that you all that has happened. Even with the truth, you will need to decide if continuing with this person in you life is worth it.
All of this is YOUR decision, she doesn't get to dictate terms or conditions to reconcile.
FWIW, I did R, but D or R is a personal choice, they both come with pro's and con's. You can't have an R without two people working together on and M. I wish you well.