@Kaiser92 If her testimony were true, she'd have seen the body from a distance and immediately screamed. She wouldn't have peered in to closely look at the Aztec knife, and thus wouldn't have recognised it when Shinra showed it to her.
Also, she couldn't have known that the Aztec Knife belonged to the victim because he only received it on that day, as evidenced by Shinra since he said that if the victim had had the knife before, he would have shown it to Shinra earlier.
Therefore, the fact that she both recognised the knife as the victim's and that she correctly identified it as the murder weapon is because she was the murderer.