Please don't propose to a woman who doesn't want to be proposed to. You're making this all about your needs and not respecting what she wants for herself.
There are a number of reasons people don't marry
I have been married previously and won't ever marry again. It's not because he was an arsehole - it's because I've realised that I will never again make the promise of "till death do us part" because I know now that I have limitations on what behaviour I will accept. If a guy knew this about me and proposed anyway, I'd think poorly of him for asking me to commit to an institution which I no longer believe in. That being said, I'm very happy to live defacto and have been doing so with a wonderful man for over 20 years now.
As an alternative to the above, I've heard many people say "I never want to get married (again)" and then they find Mr/Ms Perfect and change their minds very quickly. Honestly, I've seen this happen more times than I could count. It could simply be that you're not the One.
However, if the reason she doesn't want marriage is truly because she is so damaged, then she has no business getting married again until she's done the counselling and hard work to face a new marriage with a positive attitude. What is she doing to get over her issues.
Lastly, Breathe says that if you do propose to make it romantic. I'd put the caveat that it should only be romantic if she's a romantic girl. Some girls cringe at romance and would much prefer a casual "hey, do you reckon we should get married?" And some other girls feel that marriage should be the result of a discussion of equals and not at the request of the man.
Tricky stuff is this marriage business.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.