We can only tell you our perspective . You can't make your daughter believe differently. You can't make unreasonable ex family fight fair. We don't know situation, just what little you've told us, and only one side of the story. Kids end up estranged from parents for all kinds of reasons, this just being one. Many times exes poison the minds of children against the other parent or side of the family.
I'd tell you that desperation and frenzy won't serve you well. A good attorney might. Ultimately though if your daughter has been poisoned against you, the only thing you can probably do is to love her and be a great example for her and hope she sees the difference between you and them over time. You can't make people believe what they don't want to believe.
Don't attack her religion in front of her. You will only put her on the defensive side and raise her shields. She'll dig in deeper.
There are JWs that play fair about kids in this scenario. Others are assholes, but you can't even always blame that on the religion. It sounds like you're up against not just a dysfunctional cult, but a dysfunctional family on the other side too. I'm not sure there's a magic bullet here. Get legal counsel, maybe a child psycholgist of some sort could help.
I'm sure others will be along to help. The more information, not emotion, you put out the more chance maybe someone sees something that sparks a thought or experience that could help. I understand why you're devastated and I would be too. Again, I'm sorry you're dealing with them on both the JW level and the messed up family one.