It's not really a Pick Me Dance because I think the A is pretty much done for.
Brother I'm sorry you are here, listen regardless of the circumstances your WW is still a proven cheater and liar, so IMHO the standard advice still stands.
I discovered WW had been having an EA with a co-worker for awhile, and it became a PA within the last month
I hope you didn't just get the PA part from her, cheaters lie and minimize, workplace As typically go from 0 to 60 very quickly, often within days, they're notorious for "quickies during lunchtime".
It's more like Pick Me not D.
Based on what you wrote you don't even have a firm conformation the A has ended for good, they still work together and it could easily go deep underground, but regardless of that, It's still a version of the "pick me dance" which NEVER WORKS.
Listen lots of posters when they come here think their situation is "unique", typically the only unique thing about it is that it happened to you, just look at your member number, in fact we've seen countless of stories just like yours here on SI and other forums.
At this point your old M is gone, she's gone, no she's not remorseful, what you're seeing is probably regret of getting caught, she had choices, she doesn't need your permission to D, she instead chose to cheat, if she's truly checked out and doesn't want the M then I suggest you file for D, you can always stop it if she comes around (that's a big if), but if you want to have the best shot at R, there's a saying here that "you have to be willing to lose your M in order to save it", so here are some of the basics:
1) Full Exposure: Expose her with all family and close friend and of course OBS (Other Betrayed Spouse)/GF if any, exposure typically kills the "beautiful, exciting and romantic" aspects of an A and replaces it with pure shame and embarrassment, the more she hates the A and her huge betrayal, the more she will have AP, it typically helps with remorse. If the A is still active, 9 out 10 times the OM dumps the WW in an effort to save his own M. OBS will typically provide a second set of eyes to help with NC.
2) She needs to send an NC FOREVER message to AP in front of you, no sweet goodbyes, therefore if OM doesn't quit, she needs to find another job.
3) She needs to offer full on demand access to her phone and all electronic devices and passwords FOREVER, no questions asked. Don't buy into the "oh it's my privacy" BS.
4) Demand she gets tested for STDs/STIs (you should too), besides sex, some diseases can even be transmitted via saliva and other means, also a pregnancy test may be in order.
5) Consult a D attorney to know your legal options, knowledge is power.
6) She needs to go to IC to find out her "whys", you falling on the proverbial sword and taking all the blame is not enough.
Also just fyi, WW, child and myself will be on a week long trip to stay with her family for the holidays starting tomorrow (great timing right)
Brother I'm sorry but I don't think you're grasping the severity of your situation, this is no time to play happy family and save face in front of her parents, you're in the fight of your life, I suggest you cancel the trip or at least cut it short by exposing her huge betrayal with her parents/relatives (read "Full Exposure" above).
This is just for starters, others will chime in with more advice, keep posting frequently, the collective wisdom of SI could help you go through this difficult situation, we've "seen" it play out THOUSANDS of times.