The prevailing opinion so far is to cut them loose, but it still seems to me that the shoots can be saved. I would send her a note explaining that you'd be happy to work something out, but that you need to know more about her unhappiness before you can make an informed action. Specifically, how many images she was expecting from a guerilla shoot (I still don't know how many you took), what you can do to make her happier with the results of that shoot, and why, if she's unhappy, she still wants you to shoot the wedding. Tell her it's not about the money, and it's not about deposits or contracts. It's about having her be happy with the images from her engagement, for the rest of her life. What can you do to make her look at those pictures ten years from now and be happy with them? Reshoot? Reprocess? Give her more of them?
If none of those work (or you don't feel comfortable asking her those questions) then you should indeed bail.