I have first-hand experience with this so please read on. I wouldn't do it. Our kids are small for such a short while! Even though it doesn't seem that way at this time, your daughter will be starting kindergarten before you know it. Attachment parenting is a decision we make and it is a long-term commitment. If you had to go into the hospital for a few days, of course you would have to leave, but barring an emergency, mother and baby are a unit, and they are meant to be a unit. Especially at the age of 12 months, when babies are starting to realize their own autonomy, and fears and separation anxiety can start to develop, I wouldn't risk it. It isn't that she would be in bad hands, because she would not. But you are her mommy. You are the one. You are it. And you are breastfeeding! And co-sleeping. Of course it will be traumatic for her, and I think you know it will, because nobody knows your daughter like you do.
We always have work to do on ourselves. That is an ongoing journey. As we get older, we just become more aware of it. And life and marriage do have ups and downs. We live in a "me first" society, and you can see the results of that everywhere in this country. You do not need to go away to work on yourself. You said that you have the opportunity to go to a self-help seminar. Is it free? I doubt it. So it isn't an "opportunity", it is a consumer product you would be purchasing.
If you decide to go, I'm sure your daughter will live through it. You may even end up seeing it as beneficial. It just seems like a bad time to deviate from your commitment to attachment parenting. Undoing a lot of what you have done. One night or even two might be okay, but 5 nights and 7 days is a lot. I speak from experience as the mother of four. When my first was 11 months old I went away for a long weekend and left him with my husband (a good dad) and my mom. BAD IDEA. I really felt I needed the time away, but if I could go back and do it over again, I would never have gone. I could tell it changed him. He is now 23 and he was my most anxious and sensitive child, things I did not see in him before I went away but that were there forever after. You can bet I didn't make that mistake with the other three. It didn't ruin him or anything, but it did affect him and change his basic nature. It absolutely did.
All of the ladies who are urging you to "do it for you" are well-meaning, I'm sure. Just consider all the ramifications. If it does affect and change your daughter, are you prepared to live with that knowledge for the rest of your life? You want to talk about a head trip? Nothing is worse for you, your psyche, your peace of mind, than mommy guilt. Just something to seriously consider.