Emma magically reverts herself to a toddler, with her adult memories, but is unable to communicate and no one knows who she is. Regina takes in the lost baby girl and bonds with her, eventually telling her personal things, having no idea she's actually talking to Miss Swan, who is hearing everything, and it changes how she sees Regina (in a good way). Swan Queen ending for sure.

Swan Queen AU. After a vicious attack leaves Emma nearly dead and extremely psychologically damaged, Regina magically wipes her short term memory and takes on the task of caring for Emma during her recovery, and Emma finds herself connecting with Regina in a way she never thought possible.