I have re-read all your replies, which have been so helpful. I see my daughter, and look after her toddler, for a few hours every week, but haven't mentioned her letter yet.
You have all offered such insightful advice. The poster who said that I sounded sad is right.
I find it easy to hug friends and family, but even when I do hug my daughter, or kiss her on the cheek, there is no response. As far as I can recall, she has never hugged me, or kissed me on the cheek for years. My daughter-in-law is not particularly physically demonstrative, but she often hugs me when I arrive or leave their house. Yesterday, a friend of my daughter was at my daughter's house, and when she left she came and gave me a hug. My son-in-law will give me a hug, or kiss on the cheek when I leave their house. I just find it sad that my daughter is not comfortable with showing me physical affection.
Her father and I divorced years ago. It didn't happen straight away, but we have a comfortable relationship now, so this is not a dig at him, but it hurts that my daughter is comfortable with hugging him, and other people, but that she never hugs me.
I wish she had written the letter, and then not sent it, which is what I have occasionally done throughout my life, but she has sent it so the advice not to ignore it is good.
Thank you all again for your advice and kindness 