Edith was a naïve girl all she cared about was herself such as whinging. She had never seen anything like what she witnessed and all she could mutter was the teacher was in her underwear.
Irma also had no recollection of what happened.
Edith only saw the other girls climb higher on the rock, she panicked and ran. On her way down she saw Miss McCraw climbing the rock without a skirt. There really wasn't much that she could have said to help the police search. Also Edith had led a very sheltered life and had to whisper to Mlle. de Poitiers what she had seen, it was not the done thing to talk directly to a man about a woman (Miss McGraw) running around without a skirt! Though I must admit she was rather irritating!
shareI agree that a teenager who panicked and left the scene is not going to be a particularly coherent witness--also, as I recall, there was some mention in the book, if not explicitly in the film, that Edith was not exactly the brightest crayon in the pack.
In the book she died very young less before her 28 birthday. She was 14 at the begin of 1900 and already passed away in 1913.-
Any thougth