I'm eager....
Did you read the letter yet, or does that happen, too, when the object is opened?
Therapy, or anything within it, isn't about what the therapist wants. I assume your T suggests you open it with her so you have support and can process it immediately, but you know your internal resources, and this is very personal to YOU, not your T.... so, yup, it's your deal. Better than Christmas morning! LOL