Hello

First of all you should have full trust and belief in your daughter. If you started thinking like that who will support her.

She can score once or twice well by cheating/copying but can't perform well everytime.

Sometimes students make mistakes in real exam pressure also,they got anxious and perform bad even after knowing the concept.

So it's happens with children's.

Try to talk her and ask gently what was the problem she faced and what happened and how it led to bad performance in real exam while she was good in test.

So talk to her like a responsible parents and so beliefs in your daughter, not this year but may next year she performs extremely well and make you proud.

Best regards !!