if you recall, Edward was disowned in Pride and Prejudice. I think there was some laws pertaining to heirs to titles, but basically parents could decide not to own children any more. I suspect he would tell his acquaintances that she had disgraced him, and let them assume she had got pregnant. as for deceiving his wife, I don't suppose for one minute such a man would consider it any of his wife's business what has happened in his life before meeting her. By putting it in writing, he has at least passed responsibility to someone else, which means it will be up to Libby and Lucius to say whether she may marry before she is 21. Not an option my mother had when her abusive father disowned her because he did not like her boyfriend, and put her outside in the clothes she stood up in. She was 17. She sought succor from her future mother-in-law after walking 3 miles across town to their house. But she could not legally wed my father until she was 21.
This is why I bang on about women learning to take decisions for themselves, and opposing abusers. If my characters give even one woman in an untenable situation strength to escape, then I've done a good job.