Just caught up on your sitch ... Glad you did not send that email, Wonka is the expert there but just reading that it struck me as a "Let me tell you what is wrong about you that you didn't know" type thing ... and I have always felt the long emails or TM never come across they way we (Mostly I) would want them to so I have always refrained.
I do relate .. and chuckle a bit about the constant "We broke up" you hear on the boards. Mine did the same, and its like its justified ... I broke up with you so I could PA the OP ... yeah .. thats all it takes, I truth darted mine one night as I openly admitted I had not known about this hidden loophole in a marriage, and looked forward to going out getting drunk and calling my next W up slurring "itsth over" just before I got naked and bed another woman. The look she gave me was a priceless one.
And its not till just recently she has admitted what she did was wrong, but still does not like the term 'affair' or 'boyfriend' yet she can not really give me an alternative to use when these topics come up ... so I will continue to use them for that is what they are.
I do not think the 'poacher' phenomenon(See Predators) is just lesbian biased .. but the angle she could have very well tried to grab you is interesting to think about. And I would wager once she realized you had character .. she would have gone back to door #2 and tried to pick that lock. You did plant a seed however, a very good one that has some truth, without saying it you basically exposed your W and her moment of weakness.
I would let this seed take root, observe the next week or so how she reacts to this and you reaffirming your boundary of OW.
As far as "Did I do the right thing' ... I think there are alot of goods that I seen on this ... now how W reacts is all on her, you were honest, said things you needed to say, not to get a reaction or movement from her ... even if its the wrong thing .. nothing you can do now .. what's done is done, move on and stay on your path.