I think you start with that, and see how it goes. Takes the pressure off her, and you, too - for that matter. Being friends is not really all that simple. If you are a good friend, and feel an attraction as well, the chances are better, I think, that you will act responsibly in romance.
Also, to be blunt, you will need to regain her trust.
Please note that I am not saying that you need to walk around feeling guilty. With any couple, each will sometimes do things that hurt the other. If the hurt can be forgiven, you learn from it and go on. In time, your relationship may be better than you thought it was at first.
It will be honest.
The main thing that I got from what PDM said is that if she does not want to have a romantic relationship with you, can you be "big" enough to be a good friend?
And if you think you're not quite strong enough yet for that, tell her so, without emotional blackmail.