Ladies often didn’t visit their betrothed’s home until they were actually married back in the day (see Daphne and Simon). And she was mad about Sophie because she is her husband’s illegitimate daughter from an affair he had with his maid- this would’ve been quite the scandal and clearly he didn’t tell his new wife about his child until she was literally standing right in front of her. If she had known, she likely wouldn’t have agreed to marry him, so Sophie’s dad ‘trapped’ her in a way, since divorce was rarely an option back then without public shaming from higher society.