Friendship is an important foundation to build a new, deeper relationship upon.
I tend to agree with Nicole on this. Just because you tried getting her to go to that concert with you previously, it does not mean that you cannot use a similar approach again. You said she was hesitant and has continued to remain in contact with you since. Instead of presenting it like a date, maybe say that you are doing blah-blah or whatever and ask if she wants to tag along. Make it clear that it will not affect your plans if she agrees or not. Maybe it would be better if it was something where it would involve at least one other person, like an old mutual friend or something and she would feel less pressure, but still creating an opportunity to continue to build a new emotional connection with her to lay the groundwork for a potential new relationship.
I think many of the principles inherent to DBing can definitely still apply in this sitch. But if you are legitimately interested in pursuing a new relationship with her, it has to start with emotional reconnection and friendship - but not unconditional friendship. You have developed your sense of self from what I have read of your story and you know how to set boundaries now. I wish you all the best and I hope you can successfully rekindle things if that is what you really want.
M: 40 W: 37 T: 20 MR: 13 S13, S9, S4 BD: 1/29/18 Sep: 4/23/18 (I moved out) 8/24/18 I come home, she moves out
If you want to get out of the hole, drop the shovel.