When Mark and Abbey are sitting side by side, Mark writes her name in a book. He spells it "ABBY." However, in the closing credits, her character's name is spelled with an "e"... "Abbey."
Enid Jaynes' character is listed as "Abbey Striker" on-screen, but the character spells her name "ABBY" when she writes it down after Mark did. BTW, it is assumed that she did indeed add the "Y." (The film cuts to something else after she writes "ABB.")
As Abby and her father are leaving on the stage she says goodbye to her love and kisses him. Her father calls her name to come and she turns to board the stage. If she's deaf why would her father call her and how could she hear him.
When Brice carves the name 'BUD' into the barn's wall it is nearly unreadable. But later when Abbey points to the writing, all of the sudden it is clear, as if written in chalk, even from far away.