Brat, I know this is so hard for you, you've got a lot of very strong advice that sounds terrifying to implement because it means saying goodbye to something that's been constant for 26 years of your life.
(Advance warning, I tend to make ridiculously long posts, apologies for that!)
Right now you are playing the pick me game - hoping that by being understanding of her affair it will run out of steam and she'll come back to her loving and supportive family unit. This honestly never ever ever works.
The thing is you clearly can't live the way you are doing now and you need something to change - you either need your wife to stop cheating or you need to be apart from your wife. The part where you mention not wanting to divorce because of your daughter is a terrible excuse to stay together and you know it. Your daughter would be far better served by two stable and loving divorced parents than married parents living on a knife edge because of infidelity.
Something we say a lot round here is that you have to be willing to lose your marriage to save it. Just remember that when people are saying file for divorce - you can stop the process at any time. Calling an attorney doesn't mean your marriage is finished overnight.
Remember that we have a lot of experience and see a lot of similar situations time and time again, and unfortunately yours is a pretty common one. We always see that as long as she knows you're not going anywhere while she's trying her thing with OM then she's never going to break it off with him. Just read through some older threads to see this kind of thing come up. I remember in this one in particular you can tell something changes in the WS as soon as the BS takes control after months/years of being passive: http://www.survivinginfidelity.com/forums.asp?tid=597339&HL=53906
On the other hand, we have seen a handful of BS file for divorce almost immediately, and their WS were knocked off the fence and begging for a second chance before the ink was even dry. There was an inspiring one where the BS saw a text her WS had sent to the OW saying "I can't wait to be inside you" and let him fly to the UK to find an empty hotel room while she was home arranging a divorce but I'm struggling to find it right now.
I promise you that the best way to take care of yourself right now is:
1 - Cancel that marriage counselling appointment. She's still actively in an affair and so has no intention of working on your marriage. The counsellor isn't going to be able to convince her to stop no matter how much you want them to.
2 - Keep at it with the 180. I know you said it's hard but just remember the main points are about proving to yourself that you're strong enough to live without her. It might not be what you expected to be doing at this point in your life but you can definitely survive it.
3 - Don't engage when she talks about her boyfriend. If she shows you more pictures just calmly say you're not interested in looking at them and keep doing whatever you were doing. Same if she tries talking about him. If she complains about your behaviour pushing her towards him at all then you say "I'm sorry you feel that way".
4 - Can you do an in house separation? If you have a spare room or sofa bed tell her it's hers now. Don't let her persuade you to do anything to keep up appearances for your daughter, your daughter knows something is up even if you think you're hiding it from her. Don't leave the house yourself though (as in don't start living with a friend or something), it can make things messy legally.
5 - Call an attorney. You can break this down into steps you're comfortable with. At first all you'll be wanting to do is find out what divorce looks like for you, you don't need to get papers drawn up at the first meeting. Next you can get the papers drawn up and have a good read of them before deciding whether to sign them or not. Don't tell your wife you're doing this, it will sound like a threat, and if you don't actually hand her divorce papers after seeing an attorney you will look weak. The first time your wife should know about this is when she has the papers in her hands ready to be signed.
But remember again - just because you have her served still doesn't mean it's over! You can cancel at any point! Hell, you can go through with it and remarry if things work out that way!
Sending strength, Brat. I hope some of this is useful.