I would write her a letter OP.
Be clear from the start that there is no expectation on her to call or meet you, but if she feels able you would appreciate a letter or an email back.
Say that you hear what she is saying about you needing to address your anxieties and you would like to do so, to enable you to hopefully have a relationship in the future, but you would like to understand from her perspective what she thinks those anxieties are.
Keep it simple, do not raise anything about her anxieties or behaviour previously, don't bring up things you did or didn't do with her as a child or adult. Keep it simple.
Don't talk about how upset you are, but do say that you will always love her no matter what and that you miss her.
Something like:
Dear DD
I hope that you and DH are well.
I am writing this letter as I know you do not wish to speak to me on the phone or in person.
I hear what you have said about us not being able to have a relationship until I have worked on my anxieties. This is something that I would like to do so that we can hopefully have a relationship in the future. However, in order for me to do this successfully, I would really appreciate your feedback about what those anxieties are from your perspective.
This letter is not intended to push you into any communication with me that you do not wish to have, but if you could respond via a letter or email, it would be very helpful to me in being able to work on my anxieties that have contributed to this current situation.
Without expectation of anything further, if you are amenable, I would like to stay in touch by email / letter, as I work on my issues, so that we can hopefully take steps towards repairing our relationship.
Again, no pressure intended at all, but I want you to know that I miss you and no matter what the future holds for our relationship, I will always love you.
Love Mom