No, she can't have too much. She's regulating supply. Your boobs will produce the sort of milk she needs - so if it's very hot, it'll be more watery and she'll be using it for hydration. Frequent pooing also not a problem, assuming she's exclusively breastfed (I mean, not on solids)
Is she very young? Sympathies about the boobs, but you're doing the right thing.
nope, you can't overfeed a breastfed baby...she is probably feeding more to keep hydrated (if its hot) and also for comfort as she is in a new place.
hope your boobs calm down in a while - they are just reacting to her feeding more, and will regulate soon. Unfortunately, you might have to go through more adjustment when you get back home from holiday.