Dominance is normal - chasing, rumbling, mounting and the dominant piggy getting their pick of hides and food first. Dominance is not bullying. (Bullying is more of a sustained behaviour which can result in a piggy becoming isolated and depressed, losing weight through not being allowed to eat, chased constantly to the point of not being allowed to rest, and it ultimately breaks a bond)
If mum is food hogging then a good tip is to scatter feed veg and pellets and not use food bowls - literally spread it all around the cage. The dominant piggy is not able to guard all the food so this enables the submissive to get their fill. Ensure hay is available in multiple places around the cage