M.R.
Have you ever heard the quote:
"We spend our entire lives outgrowing our childhood."
I don't have a crystal ball but I bet you anything your mother struggles emotionally with things from her past. There have got to be demons in her closet that keep her artificially busy with computer/errands rather than the ability to enjoy one of life's greatest joys and treasures, meaning you, a loving daughter and perfectly normal grandchildren.
Have you ever asked her about her childhood? About how her parents raised her? What did they expect of her? Would she give you an honest answer?
Your mom sounds like she has an intense need to escape from those around her. I say this from my own painful past and personal experience. My children have made the same observations and have said the same complaint to me. I had a horrible childhood, but thank God, also received some amazing therapy. I know now when I am slipping into my escape modes. They can last for days if I'm not careful. The bad habits are like old familiar friends and it's difficult to change that rhythm. Especially if she's been practicing for a long time.
You sound like an insightful woman with a sensitive and open heart. I'd be curious if your mother sees this too in you. I'm positive she wants to change, would like to change, but doesn't know how to. That's why she makes the verbal commitment to be there more often, but lacks the skills to follow through, because she is quite simply stuck. Stuck in her safe zone of behaviors that soothe her.
Being in an active, thriving, emotionaly intimate relationship is very difficult for some. She sounds to be both on edge and and incapable of knowing what to do differently.