Until we had our own DC my DSD had her own double room. We have since had two DC and for three years DD had the small room.
We have now got DS, 11months who is a terrible sleeper. DD and DS were supposed to share the big room but DS wakes repeatedly and was waking DD up. So DD, 3, and DSD, 16, now share a room and DS is in the cot in the little room. But DH wants me to move DS back in with DD as soon as he sleeps better as he thinks DSD needs her own space.
I agree that a 16yo should have some privacy and in an ideal world they would all have their own room but I think it isn't worth the disruption and DSD should share with DD. But what do you all do? She is with us Eow and one night a week. DD doesn't wake her up in the mornings at the weekend, she creeps out and finds us and DSD gets up when she wants so that isn't an issue. In the evenings we have always hung out downstairs in the living room anyway. So what do you think and what do you all do?