Actually, a report card IS a legal document, believe it or not.
It has to have a child's legal name and it CAN be used for identification purposes. School records are also legal documents. They can be used to establish residency.
However, she isn't going to be charged with a crime for messing around with her kids' report card and giving a copy to her ex. Your husband did the right thing by requesting a copy from the school and in fact, he can request that the school send him all documents pertaining to his child at any time. Expecting his ex wife to provide him with documentation that he can just as well get himself, is lazy on his part.
Regardless of that, even if she had failed a class, that should have no bearing on the visitation schedule. If she needs summer school, then she can get it with her dad where he lives as much as she can get it with her mom.
Is the visitation time in writing and is there a previous parenting plan in place? If so, then he should proceed to go to Florida to get her as agreed, with a copy of the agreement in his hand. If his ex refuses to release custody to him, then he can call the police and have them escort him to get his daughter. He may even be able to have her charged with custodial interference. If he does not have any paperwork from the court that specifically outlines the visitation time, then the police will not be able to help.
EDIT- Make sure the agreement entered with the court has a court seal on it as being officially copied from the court house. Anyone can type up and official looking document from the court and if you have one with no certification seal, then the police will probably laugh in his face if he needs their help.
If you have to get a certified copy, there will be a fee. In my state it's $12 in cash, paid up front. Calling ahead to ask is prudent.