you got a very valuable perspective from a WAW today. and there is a whole lot of valuable info in it. one of these days i'll learn to imbed text quotes from other posters here, but for now i'll use old-fashioned reference (if there's any other posters that are good with directions, i'll gladly learn this trick!)
first, you get the "behind the curtains" view that your own W will not share with you at this point, namely that of uncertainty and residual feelings of attachment. i would say this is the true state with many WAWs - although i don't claim all. secondly, and equally importantly, it tells you how important the long-term outlook is. the key thing many WAWs (or WAHs) are looking for is sustainable, long-term change. which is great, because that's the kind we all want for ourselves, too.
today's observation of W may be correct. perhaps she is in a good mood because she feels like she has had the gumption to go through with her plan. and perhaps, at this point, that grass outside the marriage is looking very green. and perhaps it will be. or perhaps it won't be so much. time will tell.
but here is what i don't think your W realizes. human sexual/romantic relationships create a form of attachment that is very hard to extinguish. there are always times in the life cycle of the relationship where frustration with partner seems to override this. and, indeed, sometimes on a permanent basis. yet, whatever this biological thing is that creates attachment, it doesn't really care about the legal status of your relationship! in our heads, in our thinking, we care and make much of it - and i'm not saying we should not. but i am saying that this residual or latent attachment does not necessarily die with the issuance of the divorce decree. and that's probably exactly why your WAW at work would be "re-attracted" to her partner if she had reason to believe in sustainable change.
i cannot and would not say to any one person that this will happen. nor is it my job in any way to steer you away from your own expectations and way you need to manage and survive your situation. sometimes "letting go" or detaching not only helps you protect yourself, but it can also provide a constructive sea change in the energy in a relationship - when it's real. i can, though, talk about something i have experienced myself and observed many times in other people - this tendency for attachment feelings to have a life of their own.
the beauty of a great GAL strategy, though, is you truly win either way. and in that sense, you are winning.