I’m sure this is very painful. Bear in mind that she has been going through the upheaval of a divorce and developing a new relationship. It occurs to me that she may think you would be judgmental and doesn’t want to deal with it. It’s also possible that what to you was a minor misunderstanding was a “last straw” for her. People don’t generally throw away a 30-year relationship on the basis of one mistake in communication. Another possibility is that she may be the kind of person who holds a grudge. Without more information, neither one of us can figure it out.
For that reason, it might be helpful if you asked your dad or another family member for insight into the matter. If she is thin-skinned and has also shunned other family members, it would perhaps lessen the hurt you are experiencing.
If, on the other hand, this is personal to you, then I think you should try one honest and heartfelt letter to her, restating your apology and laying out how much you miss her and how bewildered and hurt you are by the distance between you. Lead with your pain, not with anger. Anger isn’t likely to invite a response. You’ll have a better idea about what to do next once you see how she responds.
I wish you well.