Lydia has become a “respectable” married woman. (There’s irony for you.) She is entertained in her parents’ home as a visitor. By contrast Maria is beyond the social pale and Mrs Norris expects her to live permanently at Mansfield. (Mr Bennet takes the line of least resistance with his wife. Sir Thomas stands up to Mrs Norris.) There’s a big difference.
Like ecurb, I am uneasy at the approved attitudes in the book to both the play and the errant daughter. However Sir Thomas is the soul of charity compared to Mr Price’s reaction when he hears about it.
“But by G—if she belonged to me, I’d give her the rope’s end as long as I could stand over her.” I can’t imagine either Sir Thomas saying his daughter “belonged” to him.