Depending on the type of account you have with netflix, you can have one or more instant queues. The most basic package comes with only one queue so anytime you add something to it, it's mixed together with viewing opportunities for the entire family. But if you're willing to pay more, you can get additional queues. In that instance, when logged in as DD, you could add things to her queue that you have decided are appropriate.
Things do sometimes come and go from Netflix, but once you've added something to your queue, Netflix tracks that it was there. So if there contract expires for that viewing material and they later go on to renew it, it will reappaear in the queue when it becomes available again.