After Morgan returns from the lighthouse, one can see the bandage on her hand is barely stained with the blood from cuts she received from the mirror as she talks on the phone with her friend in New York. Just a mere second later she begins to go up the stairs and her bandage is clearly more soaked with blood.
When Morgan strikes the mirror with her fist, she only impacts one point of it as it shows where her fist struck but as she falls to the floor there is another point of impact on the mirror that she could not have possibly made.