My three year old still wants us on occassion, as well, he was just up last night wanting his motorcycle toy at 3 a.m. Usually, he doesn't actually want anything, he just wants us, but tells us something like that because I ask him what he needs. Maybe your daughter isn't thirsty, she just needs reassurance to get her back to sleep.
I have found that you have to be no nonsense and tough in your response -- I'm sorry that you want your toy, I'm not looking for it now because it is night, you have to go to sleep now and I am not coming back in, you can cry all you want but that is how it is. Don't yell, just say it in a matter of fact tone. He cried for a half hour, then went to sleep. The first time or so you try this, it might be much more prolonged, because they are testing you. You've already taught her that if she cries long enough, she will get what she wants, so it might be a little hard to undo that, but tell her it, stick to it, and when she sees you mean it, the behavior will, for the most part, end.
We also used the "after hours tickets" approach. We said that mommy and daddy are no longer allowed in his room unless he has one of those tickets. Then, they get reassurance that they will be able to call for you, and you will have to come since they have the ticket. Of course, the number of tickets are limited. I've stood outside his door and said, do you have a ticket? Etc. You would have to judge if she is able to understand that at this point, he understands tickets from going to Chuck E Cheese and stuff.
My favorite thing to say to my husband -- we are in a mini war for control, and who do we want to win, us or the kids? That helps get through the parts where you need to be a little tough.
Good luck!