could be your mum is trying to get you to stop the heroine by withdrawing all your 'privileges' when you are high. a bit like how mums deal with inappropriate behaviour with children....ignore when bad , praise/reward when good. maybe she sees food as a reward for being good (not high).
I personally have not and never will take un prescribed drugs, but I do understand the hold they can have on people. Maybe a chat with your mom when you are not high explaining that you see her reasoning, but pointing out that food is not a reward but is vital for you to live.