Do not discuss a transparency plan, unless she agrees to end the A. At that time, you can tell her that in order to heal from the infidelity, you want her to follow a plan of transparency, until you can trust her again. She cannot just pick up where the MR left off. There's been too much damage. If she's not sincerely remorseful, then she has no intention of changing. The more the W protest against it, the more likely she won't cooperate or be honest.
When the W agrees to end her A, it must be done quickly. There is no tapering off. There is no affair "closure", so don't agree for her to see him "just one more time". She needs to write a letter to OM (with the H telling her what she needs to enclose. It should meet his approval before sending it.) She should tell the OM it was all a terrible mistake, that she loves her H, and that the OM can never contact her again. She should not express any feelings for the OM. Keep it short and to the point. Then the H watches as she deletes all history of OM and her messages. She blocks OM from her phone, social media, email, etc. This is very important. If she works with him, she immediately submits her resignation and finds employment elsewhere. She cannot work with OM and just be "friends". She can never see him!
She has to agree to do what the H needs to feel emotionally safe again, and to earn back the trust she lost. The W cannot tell the H what she'll do and not do. The H lays out the plan.....not the WW. She gives all him all her passwords. She deletes any computer/phone apps that aides in affairs (that don't leave proof of messages, etc.) She has to agree that her H can look at her messages from time to time. She agrees to give accountability for her time and whereabouts as long as H needs to know. If she works with the OM or is in his social group, she must leave that employment and stop engaging in the social group. This may also require her to delete certain groups from her social media. And anything else the H needs in order to feel that she is working to earn back his trust. He may need to look at her credit card purchases, and well as other receipts. These are ways she is as open about her activities as possible. This requires tremendous cooperation from her. She needs to know it will not be for the rest of her life, but for as long as you need. It requires her to be honest, at least to a degree. I know that there are other ways to deceive, but if she is serious about saving the M, then she needs to work with her H on being transparent. He is not the one who must prove anything. She is the one who was unfaithful, and she is the one who has the burden of proof. She should never get away with telling him, "You'll just have to trust me". No, he doesn't have to trust her, especially if she's not putting in the effort to show accountability.
Affairs (PA/EA/IA) are highly addictive. Even if she agrees to end her A, when she begins to crave attention from OM, she'll do most anything to make some sort of contact. Even seeing his photo can trigger the emotional cravings. It usually lasts for several months, but if she ever makes contact, it puts her back to square one again. If she'll follow the transparency plan, she will gradually lose her emotional feelings for the OM. Most WW's are not keen to any transparency plan, but it is needed in order to hold her feet to the fire and get her through the addiction.
During the transparency, the H should support his W as much as possible. However, he must remain firm and insist she follows through, even when she's being nice/sweet. He cannot trust her. He cannot just take her word anymore. People say that if the WW wants to have an A that she'll figure out a way. That is true, however, if she repents from her waywardness and the fact she brought a third party into the MR......she will need to have some type of system that will help her get back to the woman she once was. She should be told that transparency is to help her, as well as helping the H. Everyone needs accountability, especially after there has been an act of betrayal. If she won't agree to transparency, then there is no reason to believe her intentions to do what is necessary to save the M. Frankly, I don't have much hope for the WW who does not engage in transparency.
It is an emotionally rough time for both the H and W. The W will resemble someone going through withdrawals of drugs. She will get depressed, be angry at times, etc. If she acts as if she's happy and all is well on earth, then she's probably contacting OM, or he has reached out to her. The first couple of months are the hardest. It's like hard withdrawals. The time frame it takes to completely be out of the withdrawal stages will vary on the individual. If she backslides, she has to start all over again.
Withdrawals are not all the work the W will need to do to be ready to roll up her sleeves and work on the MR. She may need IC. I recommend the couple find an excellent pro-marriage therapist, preferably one who specializes in healing after infidelity. The couple who doesn't get guidance from a professional, stands less chance of staying together, IMHO. She has too many issues that need to heal. He will discover that many feelings will hit him after she agrees to work on the M. It's almost like a delayed reaction, and many H's become a WAH, if they don't receive help.
One more thing about the transparency plan. I do not recommend the H asks the W to let him see her phone. I don't recommend he looks at it at the same time, or even every day. She's too smart for that. Look at her phone when she doesn't know it, or at least, not expecting it. She should not look at it before handing it over to him. It only gives her time to delete things. And yes, some H's have be tricked this way. It's better if he just looks at it occasionally, and not make any comments. If she's not being honest, she'll eventually slip and he'll catch it. If she volunteers for him to look at it, that's fine. He can look and then thank her. He should never act self righteous, or as if he is her lord and master. He is not there to punish her. He is trying to help her.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!