Dear M.,
Mine's only 6 months old, but he's been sleeping through the night since 9 weeks. A few weeks ago he started waking up because he was rolling over onto his stomach and somehow scooting himself into a corner, which would make him cry. I used the same technique to get him to fall back asleep then, as I did when I was first training him to stay asleep at 9 weeks:
I would tend to him and do whatever was necessary to get him to go back to sleep, but UNDER NO CIRCUMSTANCES would I ever pick him up or feed him. Usually just some soothing, stroking, shhhhing and the pacifier would do it. I didn't even talk to him, because that would stimulate him and cause him to stay awake longer. The person that gave me that advice (the best advice I ever got, by the way), would turn on the vibration in her bassinet to get her son to go back to sleep, but I didn't have that option. A couple of times I played soothing lullabies on the CD player, but usually it was just stroking, sssshhhing and pacifier. At first, I had to do it repeatedly for a long time. Then on subsequent nights, the time he was awake was shorter and shorter, and now he's back to staying asleep again.
I have read that there are these "reverting to waking up in the night" phases and that you just have to be patient when they happen. And that was the case with me. If, however, you end up feeding your child, you will establish a pattern that can be very difficult to break. Your baby does not need the food, as long as she's gaining weight properly. A friend of mine's baby still wakes up at 2 a.m. in order to get milk, and she's 3 years old now.
I sure hope that helps. It will be difficult the first few nights, but it gets easier and easier, and is so worth it. Good luck!
B.