My elderly father died recently. Now my mother, who has definite narcissistic tendencies, is pushing me away. What should I do?

My mother and I have never had a very close relationship. She was not very nurturing and almost always made it seem like being a mother was a chore she just was not up to. I have 2 older sisters and they feel this way as well. We each live far away from her (because of jobs) and so are not able to be there in person to support her after my father's death 2 months ago. We all came initially and left at staggered intervals to try to have someone with her for as long as we could. Since then, we try to call her often and want to visit as much as time and finances will allow, but she is pushing us all away. When I call, she cries and says I couldn't possibly understand how she is feeling, and that she is all alone with no friends and no daughters living nearby to help her. I have tried suggesting counseling and she refuses (she doesn't want to tell a stranger all her problems). I have tried suggesting volunteering or going for a walk or reading or even cleaning out the cupboards just to get her mind off things for awhile, but she is not interested. She says she just wants to sit in her chair and cry. Twice in the past week she has hung up on me and told me to just leave her alone. This has been incredibly hurtful. I understand that she is grieving the loss of her husband of over 60 years, and I want to help her, but I am at my wit's end. She has said some incredibly hurtful things and doesn't seem to even consider that I might be feeling bad over the loss of my father. My sisters are experiencing similar things. What can I do? Do I stop calling? Write letters instead? Make another visit? Or do I try to give her space? (Please note that my mother NEVER calls me. I have to call her if there is to be any communication between us. It has been that way for my entire adult life) Advice please, if anyone has been in a similar situation. I am so upset over all of this-