Oh Karma, I am so sorry to hear your news.
I have a little inkling of an understanding of how you feel - but it is only slight. I was never close to my dad, they divorced when I was 5. I'd see him on and off, but we never really 'bonded'. He was always very critical of my size, lack of sportiness etc etc, and contributed (I think) to alot of my issues about myself and my weight. On Boxing Day last year he died, out of the blue and I felt so cheated. Of course, I had seen him much more regularly than you had, but I still felt I never got the chance to rid all the issues between us. I felt so angry that he left me carrying all the angst and emotion that had been swelling up over the last twenty plus years - and there was no one there to help resolve any of it.
I had the whole 'do I go to the ashes' thing - they scattered half of him down in Cornwall, which is a good five hours drive from me. I'd never been to his (and his family's) house down there, and in the end I decided not to go. I knew it was going to be hell either way (my step mum hates me, always has - and has been a driving force in my dad and I rarely seeing each other) with my s/m judging my choice... but this is about you - don't think about what other's will say if you do choose to go to your mum's funeral - be selfish - it is nobody's business but your own.
Feeling anger, relief, guilt etc is all perfectly normal, so don't beat yourself up. Scream at her, cry, shout etc... imagine she were there and tell her everything you wished you had when she was here. It's an emotional exercise, but you've got to do what makes you feel better.
We only did the 'local' half of my dad's ashes a few weeks ago - I stood by where we'd scattered him and asked if he was proud of my new figure...did it really change me that much??! Why did life have to be about all the negatives - he really did mess up the chance of getting to know someone pretty ace by being fixated on that. His loss - and your mum's - not our's.
I hope this helped some. Here if you need to vent - PM me.
A xx