You mentioned that this person continues to watch what you post and scoop it up - you might want to revoke her access to your tree (you can do that on the page with the list of all invitees). At the least, you may actually hear from this person when s/he realizes the link for access is not working any longer.
Here is a possible explanation you may not have thought of - when my personal family tree was still public, someone with an ambiguous username and tree name swooped through and in only a few days,copied many photos and documents related to close family (grandparents, aunts and uncles, etc) to a private tree, but ignored all attempts to make contact, even when I said that I had more that had not been posted. I eventually came to the conclusion that I was dealing with a professional, who was not about to put me in contact with their client, probably because the client might question whatever they were being charged for just copying my tree. It's possible you're dealing with a similar issue.