CBM,
If you and your wife have both read Dr Harley's work, then she already knows that the first thing he recommends in order to recover from an affair is that the wayward spouse end all contact with the affair partner for life.
It is not at all uncommon to find continued contact after it has supposedly begun. Dr Harley recommends that NC be established via letter, written by both of you and mailed together. This letter should not mention any remorse at parting, discuss the possibility of missing the former lover or any such sentiments. It should state simply that what happened was selfish and is not to continue and that the WS has decided to attempt recovery with their spouse.
AS for how long to Plan A: Dr Harley suggests that a man can usually manage about six months, while women can only make it about 3 or so. This is because men are basically more competitive than women and can keep up the competition for their wife with OM for a longer period without burning out completely.
Beware the desire to spend all of your time together discussing the relationship and working out problems. This is not really part of Plan A, though it must be accomplished as part of recovery.
IF you can do so without love busting, attempt to establish a clear boundary that stops all contact between them. You cannot demand this, but can state your own boundary on this matter. It is a prerequisite to any attempts at recovery. As long as she is in contact, she is not really working on the marriage, but trying to play it both ways. This is right from the WS handbook, so don't feel as if it is unique to your situation.
If you haven't already done so, read these Q&A columns>>>
Steps to recover from an affair. <<<
Keep in mind that Plan A is not about recovery. It is about making the WS see you at your best and giving her a reason to work on the marriage. During Plan A you should learn to make changes to yourself and demonstrate those changes by your actions rather than words.
Once real recovery begins, after NC becomes real and a period of time passes sufficient for the WS to complete withdrawal, since an affair causes many of the same chemical reactions in the brain as an addiction to drugs or alcohol, then you can try to solve all the problems. During Plan A, remain focused on making changes to you that can show her what a marriage to you can really be like, should she actually stay and work it out.
Plan A, should only last until you can no longer sustain the effort, since it is about you meeting her ENs while expecting nothing from her in return. When she is fully committed to recovery, the real roller coaster can start. You will have up days and down days, some very down days and some days you will feel like quitting.
Try to see if you can get her to send a NC letter, with the requirement that you must approve it before it is sent. Do not let her end it in person or even by phone, though phone is better than face to face.
Snoop as much as you can to verify NC is real once the letter is sent. Even when a WS means what they say, they tend to fall back into contact quite often, so for a while, you will need to learn the truth on your own.
Also read the first few posts pinned to the top of the Just Found Out Forum under the Infidelity Boards. If you want lots of input, post in General Questions II over there. If you wish to keep a lower profile, here or JFO is as good as any.
Mark