1. She's let me see her phone with no complaints.
That's good. However, it's a very strong possibility that she already deleted the stuff that she thinks would send you over the edge to divorce. And it's also a pretty good chance that she is continuously sanitizing or finding other ways to communicate with him.
2. She's been in counseling since June. It was originally to try to stop (didn't work) and is now to work through her own issues.
Therapists are fucking worthless when a cheater doesn't want to make a real change. And when it comes to "treating cheaters" they are of very questionable value even if the cheater does kinda want to stop. Read around; lots of stories of therapists with questionable moral stances on cheating, advising to hold back the whole truth, telling cheaters they did it because their "needs were unmet" and a whole host of other bullshit.
Remember, a therapist needs repeat business to pay the rent and cheaters/liars hate accountability, so a therapist who is getting paid by them is not a dependable source of hard truths.
3. She can't be continuing the affair in person at this point. She turned on tracking in Life360 (she had turned it off to hide her tracks). He's far enough away from where we live that it would be obvious. She does not and has never worked with him. I have no way of knowing if she's talking to him outside of her phone, of course.
Sorry, you need to be more suspicious. You mean he can't travel closer to you to see her? There are a million different ways to make it happen.
4. She swears they were safe the whole time, but...
100% a lie.
5. I have no way of contacting his wife. He told A that they were in the middle of a divorce but I don't know that I believe either of them.
Moe lies or bullshit. Do you have his phone number? his name? I guarantee you that you can have his wife's information by tomorrow. I'll PM you.
6. She has been open about everything as far as I know, even when the answers were terrible.
Yes, like telling you they practiced safe sex. No, she is lying, minimizing, and omitting. It's just that even while doing those things, the answers are still terrible.
7. She hasn't seen him since July, but she was planning on seeing him the next weekend when I confronted her.
The second part is true, the first part is questionable at best.
Why did I go through all of that? Because your wife is quoting chapter and verse from the "Cheater's Bible". If you start by being skeptical of everything she tells you, you will find yourself a lot closer to the truth.
The point here is to understand what has been inflicted on you, and then you have to decide if you can accept a life with the person who did this to you.
And if you decide you want to try, she has to essentially undertake the hardest mission of her life, which is to win your trust and respect back.
And even if she does everything 100% correct, then you might, at any time, decide you can't go on.
These are the fruits of cheating.