Our kids were "night trained" by the time they were about 4. If you can figure out when they are having their accidents, it makes it easier to help them. Here are my recommendations:
First, get a plastic sheet; there are going to be accidents.
Second, don't use pull-ups. Help her feel like a big girl so the accidents matter.
Then, make the last drink at dinnertime. Be sure they go to the bathroom before bed. And get them to use the toilet before you go to bed and first thing as soon as you get up.