Look mate, everyone makes mistakes. If you can overlook this and you and she both want the relationship to work, then work on it, get past this and live a wonderful life together. Don't get all caught up in the details. You can't pretend nothing happened but you ALSO don't have to turn it into Hiroshima.
If not, then do what you need to do to move on. The fact that she felt guilty should tell you something. Look at this an an opportunity to fix what needed fixing or to get out of something that couldn't be fixed.
Mistakes happen. Stupid, foolish mistakes. Doesn't mean they don't love you or that they don't wish it hadn't happened or that things can't be fixed.
No matter what you decide, don't be a fool and don't be foolish.