Wow lost, that is a difficult situation. However, I do not believe that an 8 year old is ready to make decisions based on their own best interests rather than their feelings at the time. I also believe that it establishes a pattern to allow her to make these decisions as she grows. So if she gets pissed at mom in 6 months will mom simply let her come stay with you? No, because you just don't do that.
IMHO, I would stick with your joint plan. Talk to your daughter and hear what she has to say. Then explain to her that you are going to look out for her and that it will stay the same. See if there are some things she would like to see change to make this more comfortable for her. Work with her on what will make her feel more comfortable with the existing arrangment besides staying with her mom every week.
