My wife makes soap too, but she's not done since the kids and school. This is a good idea, and a great way to get her making it again. She also brews and makes awesome wild berry wines.
I think you'd add the hops when you're pouring the soap into the molds. We still have some Oatmeal soap around and I think that is how its done. And let me tell you that stuff scrubs the crud out of you!