why test at all?
I am not a teacher nor do I play one on TV. However, I do have a suggestion for you. Don't worry about her rank. When, or if, it becomes important to her she will again make the decision that she can pass the test like she did before. She may not need the outward validation of a different colored belt.
The rank is not what is important. What is important is if she knows the technique. If she performs like a 1st kyu but wears the belt of a 5th kyu the other people in your dojo know how good she is and if they need help they will ask her because she knows not because of her rank. Likewise in the "outside world" an attacker is not going to stop and ask her rake before attacking.
I don't think that you don't know this but it had not been said.