My mother makes me feel so guilty?

How do I cope with the guilt I constantly feel from my mother? She either explicitly or implicitly implies the whole time I am not seeing her often enough, not close enough, not kind enough, not calling her often enough, etc etc. My Dad died 2 years ago and I am an only child. I have always been quite close with my parents in some ways, but I would say enmeshed would be a more accurate word than truly close. We have never had a very equal or adult type relationship. I have never felt able to share my problems or deeper feelings with my mother. She has always been a stressy/anxious kind of influence, rather than a calming, maternal influence. Looking back I think she lacked real maternal instinct in some ways. She would be totally shocked and devastated to hear me say that, because she would feel she did a good job and seems to blame me for any inadequacies in our relationship (I'm cold, I'm hard, I don't love her, I'm not attentive enough, etc). She naturally adopts the victim role. After my Dad died she and I had a lot of trouble finding the new balance in our relationship. For the first year or more I was seeing her more than once a week. There is no doubt this was (is) an awful trauma for her. My Dad was everything to her and his death was utterly devastating for her. I felt enormously sorry for her and perhaps as a result I totally failed to set boundaries. Soon I felt like I was drowning in her bitterness and resentment. She has a 'life has been mean to me' attitude, an almost zero social network, and she just allowed herself to vomit out all her pain and anger all over me, exclusively. I am not afraid of people's emotions and had she found a way to be sad with me, I could have coped. Her way was to be sad AT me. Eventually when I felt totally suffocated and miserable and I was at the point where I would have to break off all contact with her to preserve my own sanity, I tried to have it out with her and make her understand what her behaviour was doing to me. It was partially effective, she backed off a bit, but gradually some of the same problems have returned this year. I have been partially successful at setting better boundaries, but she still has the power to ruin my day. I would like to find a way to control my own guilt reaction, because I have come to the conclusion that I basically will be unable to alter her behaviours.