M.S.
Tough love. I would keep bringing her back to bed. Repeat intill she stays in bed. Eventually she knows that Mom and Dad are not gonna give in and this is where she needs to sleep. Don't rush in to every noise she makes either, my Husban does that. I let her wimper or cry for 5 min before I go in and usally she falls back to sleep before I need to even go to her. Its so hard and it rips at my heart cords to listen to them cry, but really its the best for them. It is only a phase, and you'll both get through it :)