Hello. Your question is incomplete, which makes it difficult to answer, but we can consider that the girl's experiment went wrong because she used a DNA sequence that only corresponds to introns that are not capable of encoding amino acids. Therefore, you could explain to the girl that her experiment did not work, because the introns do not encode amino acids, which prevents the clones from developing proteins that are essential for their survival, since the amino acids are the protein-building molecules .
Introns are important for the control of gene expression, but they cannot encode any amino acid, without which the organism cannot survive.