You know what, I think that if you feel this strongly about it - you should go ahead and contact her. I don't see anything inherently wrong with reaching out to your ex-therapist, and since this person IS a therapist, they should be fully capable of enforcing their own boundaries if they don't want to be in touch.

I don't think you should stalk them, or send them a thousand messages a day, or continue to send messages if they ask you not to... and I think you need to be aware of and OK with the possibility that they might not be interested in staying in touch, but other than that... I don't see any harm in you sending a message saying, "hi there, I just wanted to get in touch and see how you're doing" (or whatever you'd say).

I don't do FB, so I'll refrain from guessing whether it's an appropriate medium for that!

To answer your original question, I'm not in touch with any of my previous therapists, but I really didn't have great relationships with any of them. I am trying to contact the last one to get a copy of a consultation report that I think she may have, but haven't gotten a response. But, my current T sent out an email at Christmas time (apparently to all his past and current patients? I'm not sure, addresses were hidden) - and at the end, he asked people who haven't been in touch for awhile to drop him a line and let him know how they were doing. He said, "I truly want to know." Awww. I thought that was kind, so who knows, your ex-T may not want to develop a non-professional relationship with you, but she might be wondering about how you are!