The total money given ($20.00) - the change given ($4.51) = $15.49 is the amount Anna should have gotten.
Let's begin by now comparing the estimated change of $15.49 to Anna's $14.51 claim.
The clerk should have handed Anna $14.51 in change instead of $4.51, so, Anna would have gotten $24.51 in total. Anna could not have given the clerk $24.51 in change, though, as she only gave her $20.
This calculation shows that Anna was correct to receive $4.51 in change from the cashier. The $14.51 that Anna claims is untrue.