First a little backstory, My SO has a 6 year old daughter that we have every other weekend. We moved into a new house about 6 months ago and the transition has been fairly smooth (a few numbs here and there). About a month and a half ago we started having some issues of her not wanting to sleep in the house with us, saying that she misses her mom and she wants to go sleep at her moms house. We've tried to comfort her, sit with her, let her call her mom, etc... but all that happens is that she works herself into an emotional frenzy and would literally not sleep the entire night. Most of the time my SO decides that her getting sleep is more important than her sleeping here and he takes her to her moms house for the night and picks her up in the morning. I can see he is devastated each time this happens and it takes an emotional toll on both of us. I know is not personal and probably a phase girls this age go through, but part of me is concerned that she is dealing with a lot of stress with her moms current situation.

Here is the situation outside of our house:
Two years ago, my SD and her mom moved about 3 hours away to move in with her BF at the time and they ended up getting married the following year. As far as we knew things were going well, she called her step father "dad" and she got along well with his daughter who was the same age. In December we found out that she was pregnant and she's due in August. In January BM informed us that she is leaving he husband and moving back in with her parents near us. She told my SD that he step dad has a long business trip and because she is pregnant and cannot stay home alone (it was a very elaborate lie). From the time they moved up until a month ago, SD was getting bits and pieces of the truth until finally BM explained that her and step dad were getting a divorce and they were not going to go back and live with him. She took it about as well as you can expect for a 6yo.

Now for our current situation. BM has lost all discretion when it comes to taking about her soon to be ex. She frequently calls him a really bad guy, there's a lot of drama surrounding their divorce and even more drama surrounding this impending custody battle. She has pretty much stopped shielding SD from any of this information. SD tells us things like, step dad isn't a nice person, he hurt mommy, mommy is afraid that he will take the baby from them, etc. It really breaks my heart that she has to know these things, even if they are true. From what we hear directly from BM, their custody battle is already ugly and getting worse as her due date approaches.

I honestly believe that the recent desire to always sleep at her moms house is due to stress. She feels safe if she's with her mom and she's afraid that when she is gone something bad will happen to her mom. She is really attached to her mom, possibly to an unhealthy point, but she is still very young. She is also really protective of her little brother and I suspect as her mom gets closer to her due date SD's stress is increasing. The issue is that BM refuses to think anything she is doing or saying is wrong and the issue must be with something we are doing because she doesn't have any issues at home with her.

We have been trying to talk with SD to see what we can do to help her be more confortable and feel safe in our house, but every day it's something new that is an issue. The closet door needs to be closed, her bed is toning, her door is near the top of the stairs, the bathroom door is open, it's too dark in her room, it's too light in her room, etc. At this point I don't think that there is anything specific that we can do other than stop having overnights in our house for the time being to eliminate that source of stress all together. We are worried though that if the underlying issues are not addressed than she will only get worse.

As much as this situation is taking its toll on me emotionally, it's really hard on her dad. He had sonnyxhbhope that then moving closer would allow for him to build a real meaningful father/daughter relationship and this situation is doubting that and breaking his heart. We are stuck and want to help SD overcome her aniexty and stress going on in her life.