I had such good luck here identifying an old gothic mystery, thought I'd try with this Regency romance:

I read probably in the late 60's as a teen on a  hot summer day.....heroine is ravished (willingly) by hero, a notorious aristocratic rake; caught by heroine's father (a mill owner, innkeeper, country squire or some such, not nobility), hero is forced to pay compensation but won't marry the girl since she is "beneath" him (literally & figuratively, lol).  He takes her to London, sets her up as his mistress, she sets out to become his wife (and succeeds, of course).

I think the author might have been Clare Darcy or Caroline Courtney since I remember reading both.  Or someone similar (NOT Georgette Heyer, I remember those pretty well).  I'm guessing Clare Darcy, since I think the title was a woman's name, like most of hers.  She wrote SO many books, I haven't found one yet with a description that rings the bell.

On, nostalgia.