I doubt that she didn't remember what happened last session. More likely, she went to the subject she did because she felt you needed a safe session this round. I know my T will often do that after a particularly intense session; the next one will be a bit safer so I can stay more grounded.

You are right though. If you want your T to fill in the blanks, you have to ask for what you need. She may or may not have been aware of exactly how your experience was for you internally, and the only way to communicate that experience to her is to actually talk about it.