Neither Romantic Nor Humorous
Aunt Hanore's only reason for existence in this book is to provide a reason to include an otherwise unrelated story in the trilogy. I found elements of this story interesting, mostly Elizabeth, but it's just not humorous. Having just read the second book, they simply don't occupy the same worlds at all. And it bears repeating that Aunt Hanore, as a character, has gone from being unhinged, but plausibly well-intentioned in the first book, to cruel in the second book, to vicious in this third.
What works about this book, the third in this series, is that Elizabeth is a rich, complicated, fundamentally good character. 70% of the way through the book a plot other than humiliating Elizabeth emerges, and it's interesting.
But in the meantime...over half of the book is spent with Valen, and the deliberately cruel Aunt Hanore, belittling and humiliating Elizabeth. Valen sees evidence of her true character and while he backs off of one form of humiliating her, continues to be verbally abusive. Her twin brother, who is supposed to be so close to her that he can hear her scream when he's nowhere around, never comes to her aid.
In theory, Elizabeth's character flaw is that she seeks to marry someone who can solve her family's financial troubles. However, first, her twin--the actual heir--isn't doing anything to solve the problem. Second, there is a mother and younger sisters to support. Third, there is a home with a roof in disrepair, and fourth, money, rank, and connections were a very real part of the marriage mart at the time. It wasn't like her beaus didn't know that a penniless woman with a title whose father had up and disappeared wouldn't be looking for someone who could afford to pay off his debts and feed her family, given that her brother wasn't doing it. If she knew what they earned per annum, they knew she had nothing.
I like the direct allusions to Pride and Prejudice. The proposal scene was perfect in that regard. Aunt Hanore's comment afterwards was the nail in the coffin for me as far as finding anything remotely funny about this character.
And the marmot? The exact nature of the animal, as conceived of by Valen, is never clarified after its initial introduction as part of a longer, explicit insult by Hanore, so when reintroduced later in the book, the intended metaphor isn't clear at all. I think it's meant to be funny, but that's the problem, by that point in the book, nothing had been funny for a very long time.