My Mam also died from cancer in hospital.  I always called her Mam being born and bred in Sunderland.  Telling your Mam she could leave was a kindness and most probably made things easier for her.  Grieving has different forms and timespans for each person.  Keep talking about your Mam and let your feelings out.  I am no expert on anything and am really just trying to give you a cuddle in writing!  You might like to contact Cruise the bereavement counseling charity of whom there are good reports.  Keep talking with your sisters and other family members.  In my experience you still feel the pain even after some time but it becomes a smaller part of your everyday life and apart from anniversaries and other significant dates it becomes less debilitating. Acceptance does come but only gradually.  Best wishes.