I would not send her a message or friend request on facebook. Facebook is personal; it's for friends. If you want to send a message, I would send it to your T's professional e-mail address or call her at her work. Other than simply giving her an update about your life, I'm not sure what you're looking for with respect to getting back in touch. Did she say, at the end of therapy, that you could contact her in the future? Most Ts do not interact with former clients outside of receiving the occasional update or sending records to a new therapist. My T has told me that, when therapy ends, I can send her occasional updates via e-mail or schedule a one-off session if I happen to be in town (I will be moving eventually). She said that she only offers that to long-term clients with whom she has a strong connection. With most clients, she says there is no contact once therapy ends. I have never had contact with a previous therapist outside of requesting paperwork.