Here's a better view. I've been looking through a ton of old hallmarks but can't find anything. It looks more like the outline of a crown turned at an angle in this pic.
I would have a good jeweler take a close look at the stones. With the Emeralds they will need a serious oiling if they have been in salt water for a long period of time. That is assuming that the oiling has not been already done. Without any background to the piece it's really impossible to tell.
Also look at the cut of the stones. Are they in fact cut in the old style with the tools of an earlier era. If the other stones are diamonds they will also be cut in the old way. Any good stone cutter can help you out there.
As far as actually coming off a wreck though? Got to have more info to even make an educated guess. It is a beautiful piece though and even being able to show that the possibility of it coming off a wreck would increase it's value immensely (like if it were a beach find).
She was aware there was probably no way to find out if it was wreck "loot" unless photos or drawings were available to put it on a ship for transport. I told here I would run it past my friends here.