IHF,
Wow, I can understand what a shock to the system her letter must have been. I admire your restraint in not responding, and in wanting to meet face-to-face to discuss this, because it is a hell of a thing to try and talk about by email.
If I had to take a guess, I would imagine that 'Mr. Wonderful' who she moved in with has turned out to not be so wonderful after all. This kind of thing happens a lot; people leave someone, and then find out their new person has feet of clay, and the new relationship is not what they thought it would be. And having picked a dud, they try to hit the re-wind button.
That is something that you must be very careful of - you must make sure she is not saying all this stuff about what to come back just because her new guy has turned out to be a chump. For yourself, you really need to make sure that this is not just a case of you being her Plan B. I am very sorry to say something so brutal, I realise how sensitive and vulnerable you are at the moment, but that is why you must be extra-careful and extra-wary about her motivations.
Something else that I think needs exploring is whether she has told her new guy that she has written to you that way. I just have a feeling, based on what she did before, that she is probably messing the OM around in the same way that she messed you around with half-truths, omissions, and lies. Just as she deceived you, so she may be deceiving the OM now. I know none of us would shed any tears for him, and that is not why I am raising it.
The issue here is one of her honesty, and whether she may be messing two of you around by playing fast and loose with the truth. If I were in your shoes, and thinking of taking her back, I would be telling her to be open and clear with the OM immediately.
I cannot help thinking that she may well still be playing house with the guy, and will continue to do so if you do not take her back, which means a continuance of a state of dishonesty. She needs to change that behaviour, and start treating the men in her life with respect, and that requires honesty (whether or not it suits her). Effectively, if she is not being open with him, she has now made you the OM to the OM, which is ironic, but it is just piling dishonesty upon dishonesty, and if you are going to take her back, she has to break that habit.
It seems significant that she has not mentioned the guy, or her living arrangements, doesn't it? She doesn't say she has left him, and she doesn't mention how they are getting on.
Obviously, you will be thinking about what you want to discuss with her, but I think a key issue is this: she knew who you were, and she left you. She was not forced to do that, she did it willingly. So why is she suddenly so convinced of how wonderful you are? You are the same person she walked out on, only damaged, and suddenly she thinks you are great. I know that is what you want to hear - I have been there myself - but it's a hell of a change to convince herself that you are 'wrong' for her to the point where she walked out, and then have some kind of epiphany and decide you are great. Something is fishy about that.
Finally, and my heart really goes out to you on this, because I know where your emotions must be: please, IHF, do not convince yourself that she is saying or doing things that she is not. We always have to be careful to not convince ourselves that we are seeing and hearing what we need to hear, just because we want it to be true. Just as her letter was all about her, so your interaction with her has to be all about you, and what you need to be secure, and to trust her motivations. To do what she did took a lot of thought and planning, and she chose to do it. Th question has to be, if it was right a few weeks ago, why is it suddenly wrong?
This is not to say you should not reconcile with her. That is quite possible, though it will have its tough elements. However, for your own sake, you really have to make sure she is coming back for the right reasons, and you need to be sure that if you do let her come back, that she will not up and do the same thing again in a year's time. So if you do think reconciliation is a possibility, please do not rush to offer it. She needs to go through a process of proving why you should take her back, and explaining why she did what she did, and why she changed her mind. Doing that work, and going through that process will be cathartic for both of you. And for you, it is absolutely essential that you get the truth from her before you take her back.
My thoughts are with you, and they will be with you on Wednesday. I know where you are in this, and my heart goes out to you. That's why I urge you to be careful and cautious, and to not meet her wearing rose-tinted spectacles.