I’d say keep to the original agreement , if mom B didn’t want to spend the extra money maybe she should have thought twice about the extra food she wanted to bring when Mom C said she’d be covering the food , I’m sure if Mom A or B had anything extra they personally wanted they would have fronted those costs themselves but idk maybe my opinion is wrong
Stick to the agreement. They should have split it from the beginning but have one person sorting it. It makes sense that food will cost more.
Leave as is. Mum B was meant to buy a cake that’s it
Stick to original agreement