The Duchess, by Bertrice Small

This is my first Bertrice Small book, and I have to admit I had certain expectations.
None of them was met.
I'm sorry to say this is the worst book I've read in a long time. I had to force myself to finish it, that bad was it.
What was bad with it?
1. The plot: it was practically nonexistant. Allegra is the richest heiress in England, but doesn't have blue blood. Her mother ran away with her lover when she was a baby and her brother died with his fiancee in the French revolution, so she despises love and vows never to fall in love. Quinton Hunter is the duke of Sedgwick but as poor as church mice due to his ancester's preference for marrying for love instead of money, and he vows never to make that mistake. He decides to marry Allegra for her money, but being both young and beautiful promptly falls in love with her. He spends half the book trying to disguise his feelings instead of wooing her, but at the end she recognizes she loves him too. There's a small subplot in the last third about rescuing a french noblewoman, and that's the only action you get to see.
2. The writing: it was dreadful, completely childish. The characters have no depth, and the secondary characters are only there to show that the world is populated. A small example: Quinton decides he has to marry, and his 3 best friends decide to marry as well. Why? No reason at all, just behaving like a flock of sheep. The only slightly interesting part, the rescue of the french noblewoman, was told in such a way that it seemed only marginally more dangerous that going on a picnic. All the couples - except for 1 - waltz in and out of Terror France, taking with them a french countess, her 2 sons, and even the maids. Not to mention that pages and pages were dedicated to describe gowns and food. Sometimes it read like a foodie blog. And even the parts where Small writes about buildings or gives facts about Georgian England, it read like a copy paste from a textbook.
Where is the anguish? Where is the smoldering passion? The love that lasts until forever?