Unless she recovers her senses after getting over the shock of seeing righteous violence performed in front of her so abruptly, she isn't the one for you. You're going to need someone who appreciates that you take care of business like a man.

I would say put the engagement on “pause” - It seems there is a disconnect between OP’s values and methods and GF’s… I agree with the basics of what OP did - But once you got the ring back, did you keep beating the thief? If OP did, that’s over the top and could explain GF’s reaction. If not then GF is painfully naive and there’s the risk of future problems… Obviously two people don’t have to have the same exact viewpoint and values to be a successful couple. But this might raise a question mark depending on the details in this story… As a side note - It’s not usually a great idea to propose in a public area except maybe a nice restaurant.