People move their toddlers into beds at all different ages and for different reasons. Because she is not climbing out of her crib (which is dangerous) and you don't need the crib for a new sibling, then my advice is to wait as long as you can. We were originally going to wait until our little girl was almost 3 or for her 3rd birthday, but we got a great deal on a mattress set and did the change over in the spur of the moment when she was a month younger than 2 1/2. She did great at first, but we have gone through MANY exhausting stages since then. We have had to remove her lamp's bulb, put a door knob cover over the inside knob, keep her panties and pull-ups up or out of her room, and most recently, put her little potty in her room. She's a night-owl instead of a morning person, and we have caught her: reading in bed until 11pm-midnight, go through many dress-up sessions with hamper clothes and dumping out dresser drawers, put on ALL 19 pairs of clean panties (that one was a hoot until day three when she peed through the 17 pairs she had on), snuck out to quietly play while we watch TV in the evenings, and go though FITS at bed time because she swears she has to go potty (but "can't go" when we let her).
We were fooled at first, because she loved her bed and happened to be sick when we got it, so the first week or two was fantastic. But her new-found freedom has led to a trashed bedroom many times and horrible tantrums at bedtime. She used to be the easiest toddler to put to bed at night (outside of tooth-brushing) but now she cries when we close the the door most nights (just for usually 2-5 minutes anymore). Obviously, you know your daughter and her personality, so you'll know better with how she might do. I did think it was going to be harder, but I wasn't prepared with just how much harder.
As for falling out, our little girl also slept all over the place and sometimes we still find her like that. She has fallen out of bed a few times but only once since we have used the bed-frame (that's another story, but she was on the mattress and box-spring on the floor for a few months). Now she seems to do fine and has learned where to sleep.
As for other toddlers we know, her cousin is the same age and they moved her at 15-months (which we couldn't imagine dealing with). To this day, they still have to lay down with her until she falls asleep because they did that at the beginning because she was too young to understand (we have made sure we never did that - we might lay down for 5 minutes on a really bad night, but that's it). She has friends that were always good sleepers and pretty mellow kids, and they had their phase of trashing the room and running around until they passed out on the floor. Others had a hard time the first couple of weeks, but then were fine. One perk is that is has helped with night-time potty training for both our daughter and a friend of hers. She'll get up to go most of the night and her friend who is the same age stays dry all night now.
Plan on there being an adjustment period and that she might go through many frustrating stages. Our little girl LOVES her "big girl" bed, but part of me still wishes we waited until October for her birthday. Most nights now are really fun, though. We can all read a story in bed and we get the BIGGEST hugs and kisses now (which we barely got at bed time when she was in the crib). I hope this info helps. :-)