I have a close group of mom friends and we can and do share everything about our lives and our kids. Our kids range in age from 9 - 14 now. We discuss issues with school, learning disabilities/meds, discipline, hormones/first periods, and on and on. It just makes parenting so much easier to have a trusted group to share difficulties with, and to know that they are dealing with similar issues.
I don't think it's bad that your daughter overheard, and it's perfectly normal that she didn't like it. I would have a talk with her about friendship and sharing among girls/women. I would say that I hope she has/will have friends that she can get advice and support from.
When I was young, I had NO friends who would talk about anything personal (periods, dating, anything). It took me until I was over 40 to develop this kind of friendship. Everyone should have friends like this, including your daughter. Then she can talk about you with them...
ADDED: Of COURSE stepmoms talk about, worry about, get advice about, their stepkids, the same as bio-parents do. I've been a stepparent for 27 years and a bio-mom for 11...