Everything changes when she realizes she's pregnant.
Her first instinct is to not tell George. It's one more thing he doesn't need on his already-burdened shoulders. She can take care of it herself.
And then she thinks of Fred, and what she would do if it was his.
She tells George, and he reacts exactly how she expects him to react.
A moment's hesitation stops her otherwise planned answer.
He conjures a ring and slips it on her finger, and tries his hardest to smile at her.
She smiles back. After all, what's one more day pretending?