The terms of the challenge state that she can’t tell anyone about it before or after the duel or it goes to the Wizangamot. So, no, presumably she can’t tell Harry about it.
Heck, she might have severely injured Draco by accident, rendered basic medical care, and then just left, because she can’t tell anyone. If someone found Draco unconscious and half-dead later, and they figured out Hermione did it and left him, that would look like attempted murder.
What evidence is there that H&C isn’t just Quirrell wrapped in an illusion?
There’s no need for Hermione to have cast the lethal hex. She wins the duel, then the real perpetrator stuns both of them, hexes Draco, and then memory charms Hermione into thinking she did it. However, if that’s the case, unless the perpetrator then used Hermione’s wand to cast the hex, checking what spells her wand had cast would reveal something fishy.
Why are we proposing the H&C is not clever and powerful?