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Parents in an intact marriage have nearly absolute control over who can and cannot visit with the parents' minor child(ren). Your mother can petition the court for visitation, but as long as you and your spouse are unitied against her, there is very little that the court could do -- unless your mother produces evidence that the child will suffer some substantial injury were visitation not granted. This is a nearly insurmountable burden, especially for a parent who does not already have an established relationship with the child.
The presumption is that you know what's best for your child. A good attorney would raise the argument to the court that you are in an intact marriage, any intrusion by the court requires both a compelling state interest as well as strict scrutiny, and therefore, unless the grandparent produces some "clear and convincing" evidence suggesting that her visitation is in the child's best interests, that the court should dismiss the action forthwith.
What I'm saying is that the issue rises to a question of "fundamental constitutional rights." Judges don't often encounter this sort of thing, but when they do, they are usually loathe to involve themselves, because of the potential media attention. This is the sort of case, where if the judge were to open the case up to an evidentiary hearing, you could go to the ACLU and they would probably be interested in representing you.