While I agree that this author's books have got annoyingly formulaic, this one stuck out for me because the match between the protagonists was more of an equal one. The heroine is 29, so as a grown woman she can be something other than a tender innocent, and be a fully fleshed strong woman. While her strenghth of character might come across as arrogance, you have to look at it more from the point of view as to how women were viewed at the time, and it must have been frustrating to be treated as not terribly bright, and only useful as either a decorative ornament for some man's arm or a broodmare if you wore skirts.
Her history makes it clear that she has good reason to be strong willed and I loved her as a character. I also enjoyed the fact that the mystery was more the main point of the story though the romance, though it was far from secondary.
As for the 'lady bountiful' comment made by a previous reviewer, all the males in this author's books have workers and other 'underlings' who lives and fortunes are reliant on them because they are major landowners and practically owed whole towns and counties. Why it is arrogance for a woman to take on a man's role because she's a capable, titled woman and she has a genuine concern for the those who she would have been raised to see as her 'dependants'. This says a lot about people who'd rather have women in 19th century novels doing needlepoint or playing the pianoforte. Would that make better reading or make the reader admire her more as a character? Well that depends on the reader.