I'm not clear on whether or not your husband's parental rights were terminated here or whether the grandparents actually adopted the children or if they were appointed managing conservators of the children. If your husband's rights were terminated, despite the fact that the grandparents have allowed him a great deal of access to her, legally he's no longer her parent. It may be that until she's 18 there's nothing you can do.
However, if his rights weren't terminated and rather than a full adoption the grandparents are joint managing conservators along with your husband (is he paying child support or is that coming from the state? does he have access to her by court order?), then he could file a suit to change the court order about where she lives because she wants to move and it could be argued that it would be in her best interest to do so. I'd expect the grandparents to contest this, and to say that it's in her best interest to stay with them. This could take several months and it could be really expensive.
In any case, you and she might be better off waiting until she's 18 and she can just move out and go where she wants to because at that time she's legally an adult. They can't hold her there as an adult just because they may want to continue to collect child support for her.
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