You can't necessarily prevent her from filing and claiming her. This doesn't mean she will be successful in claiming her.
Many times what will happen is the noncustodial parent will claim the child. If they filed their return first then the custodial parents' return will be rejected when they try to claim the same child. This will cause the custodial parent to have to print and mail their return. The IRS will then use the Tie Breaker Rules to determine who gets to claim the child for the various credits one can receive when claiming their children.
If your husbands' daughter lived with you for the entire year then her mother would not be eligible to claim her.
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