Dalliard, I just wanted to share my experience and reassure you.
My DM died 6 years ago. For ages, I would see elderly ladies of about her age and think "why the hell are you alive, and my DM is dead?" Sounds awful really, but that's how it was.
The only surviving female relative of her generation on my side was my mum's cousin's wife, and I couldn't bear to see her for about 3 years (there had never been much contact before). Now I see her about 3 times a year with my daughter, and I was so sad recently when DD said "I love AuntieB, she's like a grandma". But at the same time, I am grateful for AuntieB's presence in her life.
After DM died I had to really force myself to think "at least DMil is alive for DD's sake" but in all honesty I did resent her being alive. That first Mother's Day we had without my DM almost creased me. Sadly DMil also died just 4 months later.
Even now, almost 7 years later I just can't bear to go out on Mother's Day, we always go out on the Saturday. It's just too sad for both of us to see grandma's having a special day with their grandchildren, when our own DM's and DD can't have that.
Bereavement and grief force you to endure all sorts of conflicting emotions, anger is one of them, and it's very common to feel this way. I loved my DM dearly but we also had "issues" and I was very angry about all kinds of stuff. What you are feeling is completely and perfectly natural. And it will get better in time.
If you feel really dragged down by it, do see a Bereavement Counsellor although I must say both GP's I have had since have surprised me by being very kind and understanding, so you might try that first. But give it time - there's no set time either, it takes as long as it takes!
One thing I found quite helpful, when I was really overwhelmed with thinking about DM, was the suggestion that I set aside a particular time of each day to think about her - but not beat myself up if I forgot, because it was a sign I was feeling better.
Wish you well x