Annie Our children, especially adult children are independent people, we may want to protect them, but we can't.
To what extent could your mother have protected you at the age your DD was when she died? I find remembering myself at my children's age is a good corrective, if ever I get over-protective.
DH and I lived with DD for 2 months after she had a serious accident and while she was very grateful for all the help she really needed, we got 'seen off' very quickly if we went too far in our care and she had us back in our home as soon as she decided she could manage without us, even if only with difficulty.
Your daughter was an adult. You offered her all the help you could, but she was free to refuse it, even if it was not in her best interest. You have to accept that.