An afternoon nap isn't "essential" for anybody except young children and the elderly/unwell.
Don't get me wrong, I love a nap, but it's definitely not essential for a healthy adult! And these were the child's parents, not her "travelling companions". A "travelling companion" would suggest an equal adult who has had equal say and agency in the trip, destination, agenda, etc. Children usually don't get that. An 11 year old can't go out by herself, go to a shop, the beach, pool, cafe, etc, as an adult travelling companion can if the other adult wants to do something different.
It doesn't sound like OP's DD needs to "practise patience" either - what a terribly sanctimonious phrase! It sounds like she did as she was told and let her parents rest and did her own thing in the living room as presumably she was not tired and didn't want to nap. OP doesn't suggest she disturbed them or kicked off about it.
OP asked her daughter a question and she answered honestly, as kids do. It is not unreasonable for the parents to want to nap in a hot climate, but it is also not unreasonable for the DD to have found having the day centred round her parents' afternoon nap and spending 2hrs a day by herself in presumably a small holiday apartment rather boring. I'd have loved being left alone by the other humans for 2hrs, as would my DS1, but we are introverts who need alone time, and DS1 always said holidays were too much family time and not enough space for him. Extrovert DS2, on the other hand, would have climbed the walls at 11 if left to his own devices for 2hrs a day.
OP has a choice what she does with this information. Either shrug and go "tough titties kid, the adults are paying, we run the show" - which some parents would do - or maybe compromise a little while she is still too young to be allowed much independence on holiday and save the hot sunshine holidays for when she's a bit older and can go out and about while her parents enjoy their naps.