@WTL
The interesting thing is this means her older sisters *decided* that she needed to be this big for some reason.
Colonies will produce different types of workers to meet varied conditions.
I suspect she is large so that she can store food. Camponotus pennsylvanicus are related to "honeypot ants" and the larger ants can hold a lot of food in their social stomach. She's like a living smoothie truck for her sisters.