My first thought in reading the subject line was "session, as in singular?" As I've spent many sessions at least partly on my past. My T covered some of the highlights/lowlights in our initial 90-minute intake session, but other stuff has come out over the past 16 months, as I've trusted him more. Once, maybe a year in, I did take in a list of potentially traumatic events I've been through that we went partly through. But there wasn't just one session about the past. Again, I kept some stuff from him (or at least the details) until I felt comfortable/safe. (While other things I maybe shared a bit too soon...) If you're not ready to talk about something, you can just tell her something like, "there's more, but I'm not ready to talk about it yet." Even if you've been seeing her for a longer period of time, that's completely acceptable--clients need to go at their own pace. Hope the session goes or went well.