My mum is person B but would never call anyone a bitch.
It's bad enough without swearing at your own child (and calling your daughter a selfish bitch is unforgivable in all but the most unusual of circumstances).
About a decade ago I was at a fairly expensive restaurant with various extended family including my mother. There were 12 of us around the table. We'd all had starters and main courses - my mother ordering boiled fish with vegetables, sauce on the side, but stealing "tastes" of everyone's richer dishes - she is a virtue signalling "I eat like a sparrow, ooo I'm stuffed after eating that lettuce leaf, I don't know how you can eat all that, just a salad for me" restaurant goer.
The restaurant did those tiny taster desserts - little tiny shot glass size things, barely 2 teaspoons of content.
Everyone but my mum, who declaired herself "stuffed" ordered one.
As soon as they came she was hovering over her neighbour's with her coffee spoon ready to dive in.
She had a spoon full of all 11 - (and double dipped into everyone's 
not envy).
Everyone who had ordered a pudding got half a pudding (because they were so tiny) and she ate FIVE AND A HALF portions!
The weird dynamic in my family is that my mother is never called out on anything, but that was the point at which I started calling her out on things - her response was that I'm "funny about food"
It's not me who's funny about food... 
That incident is now famous among my children, including the one who wasn't born at the time...
It's not just about food with Person B types, though there are often food issues (my mum certainly has good issues of her own) even if they tell themselves it is simply about wanting to taste something - it's very much about control and attention. Being person B makes you the center of attention in away just ordering and eating your own food does not.