How do I help my mom cope with my dad's death?

My father died in October of 2012. He had a heart attack back in 2000 and open-heart surgery that same year. For a while, he was doing great. The summer before he passed, he was in and out of the hospital. It was heartbreaking to watch someone that I love and that had always been the rock of the family, to deteriorate. Right before he died, he was actually doing very well so at that point it was unexpected. When he died, he died in his sleep. Apparently, he had a stroke and his heart was so weak that even his pacemaker couldn't get it going again. He had been sleeping in a separate bedroom from my mom at that point. She went to wake him up in the morning and he wouldn't wake up. Moving on...since that time, we (me and my 2 brothers) helped my mom move into a a great apartment where she feels safe living on her own. She loves her new apartment. She started seeing a therapist, which we all thought was great. We have all tried to be there for her but are sometimes at a loss as how to help her. My brothers live within 15 minutes of her but I am three hours away. I try to visit as often as I can and I text her almost everyday and call her all of time. My younger brother helps her out running errands with her and he and his girlfriend invite her out quite frequently. Our older brother is married and has two children and recently changed jobs so he is extremely busy but does what he can. The problem that we are having now is that what we all do is not enough for her. We will spend a great night with her and she will say that she has a great time but then two days later, we will all get an email about what she wasn't happy about. Her emails always start with..."I saw my therapist this week and she said..." Most recently, it had to do with her birthday. She wanted us all to take her to dinner and we all planned it. I ended up not being able to go because of weather and my work schedule. My brothers and their significant others took her out. She said that she had a great time and even texted them afterwards to thank them and say that she had a great time and it meant a lot to her. For her birthday, she had asked for a $200 bracelet. None of us could afford it and dinner so we didn't get it for her (but we are/were planning to get it for her at another time). She is struggling financially and we gave her a large amount of cash for Christmas. We are also struggling. Anyway, I got a text from her the other day asking about what happened to the bracelet that she had asked for. I was in shock!!! She knows that we are all struggling. Then she sent an email to all of us saying that, "I saw my therapist this week and she doesn't think that I have a good support group in you guys". It continued to say that nobody every checks on her, etc. She went on to explain a specific day that there was a big storm and most of that area lost power. Both of my brothers had but she had not. I was in contact with her a lot that day and my one brother was in constant contact with her. She said, "nobody checked on me and I checked on all of you guys. If I didn't have power, I wouldn't have anywhere to go". She had power and knew that both of my brothers did not but yet didn't offer for them to come to her house. Yes, you would need to be invited if you are bringing kids. Anyway, after this email, we are all really upset. I won't speak for my brothers but we have talked about it. I feel that her therapist is telling her what she wants to hear. The fact that her therapist thinks that we are not a good support for her is based on what she says about us. That is extremely hurtful! None of us have spoken to texted her now since the email. That has been since Wednesday. Since my dad died, I have never gone 3 days without talking to her. I am just so upset that she feels that we don't care and that we don't do enough for her. I also feel that when she doesn't get exactly what she wants (such as the bracelet), she goes on these rants. It is crazy and we should all be sticking together but every good occasion with her turns into an email about what she and her therapist think that we are not doing correctly. I am sure that she has been in contact with her therapist again since none of us have been in contact with her. It makes me sad. I am sure that this weekend has been tough for her. She is used to hearing from us. How do we make her understand?