Hmm little o not sure about that... I know that babies will generally feed more frequently than during normal weather, but it is my understanding that it is more about thirst-quenching, due to the fat content of the milk at the start of a feed being lower than at the end.

That doesn't really make sense - here's some info from the ABA website:
Breastmilk contains a perfectly balanced ratio of food and water to meet all your baby's needs. It is a living fluid, ever-changing to suit your baby and even in response to the weather! The first milk your baby gets from a full breast has a low fat content and naturally quenches baby's thirst. Once the let-down has occurred, the fat content of the milk gradually increases as the breast softens. This later milk has a creamier appearance and satisfies baby's hunger.*

In hot weather a thirsty baby may want to breastfeed more frequently but for shorter periods. In this way he is getting more low-fat milk and so is satisfying his thirst. If you need to be away from your baby, it is preferable that he has your expressed breastmilk (EBM).
I'd reckon that because she's feeding more frequently she'd get the right amount of food