I hope you see that the reason why she "collapsed" is because you followed some of the advice given here and were ready for the confrontation, you were prepared for the initial denial and then after admission, you were prepared for the blameshifting fireworks, you also exposed them to OBS and both your family and hers (she thought you were trying to "destroy" her), you destroyed their "romantic A tree" and threw a wrench at their plans, you and OBS destroyed their fantasy and she quickly learned that OM was not going to jump ship and that they would not run into the sunset together, even knowing that, she went to see a D attorney to see how much D would cost her, she was slapped in the face with the facts$$$ then quickly told you her attorney "told her" to try to work things out before she decides to cough out all that money for many years and since rich boyfriend didn't leave his wife for her, she possibly felt "trapped" with her plan B (YOU) who would also helped her keep the "doll house" appearance to outsiders at least for a while until rumors and gossip about the A dissipate. Had you not taken the great advice you received here, things could have played out very different, you tackled the A from a position of strength and did not show any signs of weakness (very unattractive btw), you didn't do the "pick me dance" (which never works), you demanded what you needed which included NC FOREVER with OM (deer in the headlights look), etc., all that has played a part of the so called "collapse".
You and OBS have seized control of the situation and appear to be driver's seat, do not lose control now and stay strong, yes in IMHO you said the "I forgive you" way too quickly but that's not unusual, you're still shocked by the betrayal, you never thought she was capable of cheating, yet she did it for months and was planning her exit strategy. Another thing, please don't minimize calling her DECISIONS "a mistake", a mistake is when you take a wrong turn on the highway that you DID NOT mean to take, she MEANT to cheat and have sex with him every single time she WILLINGLY took her clothes off, every sex act, every kiss, every text to OM behind your back was a VERY CONSCIOUS decision, her consult with a D attorney was a conscious decision, make sure you don't ever lose sight of that, she needs to undergo intense IC for a very long time to find out her "whys", you were in the same M and you didn't cheat.
I strongly recommend that you continue posting frequently at least during the initial phase, it's a critical phase and we've seen it played out THOUSANDS of times, every case is different but cheaters typically follow a similar script and your WW actions after Dday have been text book reactions, it's healthy to take a break from SI from time to time, but make no mistake about it, we are NOT arm chair quarterbacks, we have played and been played, we've watched the infidelity game thousands of times here and other websites, I honestly believe this is the best place on the entire web for advice in such an awful situation.
Please follow the advice and consult your own attorney, she was ahead of you on this and didn't even tell you about it until the very last minute and after some pressure by you of the specifics of her "appointment", btw ask her what attorney she went to go see and get proof of payment if any and make sure this wasn't an appointment with OM and one last fuck.
So far she has not even sent the NC FOREVER letter to her boyfriend (at least you did not mention it) despite your very specific request to do so, I understand she told her coach she would not be training with AP, that's simply just not enough, she even mentioned she's considering stopping altogether, I think you need to make this a requirement, you have a lot of work ahead of you and she needs to devote all her free time and energy to you and her children, another trophy on the shelf should not be a priority and like I said before, if it was me, I would have told her to abandon that particular sport altogether (at least for a year) and focus on the family. Remember she needs to offer FULL on demand access to her phone and ALL electronic devices and passwords FOREVER, no questions asked, Whatever you do, DO NOT RUGSWEEP this and just try to "move on", forget MC for now, way too early for that and have her go to IC first, I know some of the advice may seem harsh at times, but mostly it's sound advice with good intentions, the collective wisdom of SI could help you navigate during this difficult time, thousands have benefited from it.