You did great and you can feel very, very good about that. I think her hesitation about writing has nothing to do with any doubt about her caring. I think it's more that it's a daunting task to somehow encapsulate the depth and breadth of feelings shared in a one-off letter. I think it's bound to feel flat, especially if you tend to obsess over each word over time. It's taken me a long time to be able to take what my T writes at face value and allow his words to reflect him, not me. If I couldn't do that, each letter would make me crazy. I think she simply doesn't want to create a potential burden for you. I can almost guarantee you that what you will remember of your last session in the future is her calm and hopeful demeanor, her faith in you; had she expressed upset at your leaving, not only would it have been unprofessional and unhelpful for you, but it would have left you with doubts and unsettled feelings.