With mine, I skipped the toddler bed and went straight to a twin, but that's just b/c both times I needed the crib for the next baby, LOL. I pretty much just set up the new bed, with the box spring and mattress on the floor, and bed rails on the bed. That night Mommy and Daddy got in bed with them, and read books. They LOVED IT that Mommy or Daddy could actually get in bed with them. I stayed the first night until they fell asleep, and from then on I stayed a little while, and then left while they were still awake. I must note that my kids both moved into big kid beds when they were less than 18 mos old, b/c my kids are all really close in age. There wasn't much of a "transition" to it -- I just moved them and waited to see how they dealt with it, and then adjusted from there.
As for keeping them in bed, I am personally not comfortable closing their doors or locking them in, so I used a baby gate at their doors. That way I could still hear them if they woke up at night and needed me, and I didn't have to worry about them wandering through the house, or into our room.
Kids are pretty resiliant -- I suggest you just give it a try, and then adjust your expectations from there. If she takes to it right away -- great. If not, you can always put her back in the crib for a little while. Each child is different, so you'll just have to see how she does. Good luck!