Quoting Onalee's Mummy:" <blockquote><b>Quoting Jenna+1:</b>" She does it because she knows you'll give in. ... [snip!] ... only take a night or two."</blockquote> How many hours will it take for her to stop crying and fall asleep roughly?"
you don't have to do anything besides communicate clearly about what's happening.
tell her she's going to sleep in her own bed like a big girl (you can tell her about how all big girls do this and only babies sleep w/ their mama) and that crying won't change that fact.
repeat as often as possible.
if she's gulping air upset from screaming and crying, i'd stand in the doorway and speak calmly and clearly and say, "time to sleep - close your eyes, i love you, good night"
don't go pick her up, just be clear, calm and loving... and then shut the door again.
it'll take a few repetitions, but probably only a night or two...