Sounds like you guys are doing all thr right things. I think you are right that the next thing to do is to seek some help from a child's pshycologist. dont forget that you guys are great parents and you will all get through this together.

One other thing I thought of that they often get children to do to get to the bottom of issues is by drawing or through play. Maybe the 3 of you can play dolls or something and make it a really fun activity and see if anything comes up that way. Maybe ask her which doll she would like to be (mummy, daddy or the daughter) it might be interesting to see how she sees each role in the family and if nothing comes out of it then you have spent some quality time together.