Sounds like the therapy touched on things and the letter and the holidays may have triggered additional stuff that has set her off into a bit more depression. I would leave her to think about things and if she wants to talk, listen. If others ask about giving her letters or talking to her, you may want to advise them to wait a bit. She is very fragile right now and I wouldn't want to see her do something that she normally would not do.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
