There's a bit of Karen character assassination going on in this thread, so posting the below spoilers for anyone who wants to know additional details. This will likely be covered relatively soon in the manga regardless though, as its a relatively quick arc in the light novel, so you may just want to wait and see.
It's been a bit since I read the light novel, but to my recollection the basic situation with Karen is that she did and does like Auger, partially because when they were engaged he was one of the few people in her life who treated her kindly. She had no choice in the engagement being called off, just as she's had no choice in having to act like a man despite actually being fairly feminine (sorry for those hoping she'd keep the masculine traits), and the prince treats her pretty badly on top of that.
Long story short, Auger (due to his own delusions) thinks he's helping to fix her relationship with the prince but actually ends up winning the right to get re-engaged to her himself, forcing her father's hands. Karen is happy with this obviously, but really its Auger's own fault and not her doing. Since he's also accidentally more or less promised to marry Mashiro at this point, they have a bit of an argument at first, but they eventually seem to decide they can share Auger, as long as it's just with each other (and Alice). Pretty standard harem stuff all round.
And yes, she is somehow hiding substantial assets under that jacket.
I don't think there's a character assassination here since I clearly got what you mentioned the first time I saw her character. Everything was laid out in the clear when Karen was introduced. I couldn't believe there's actually people who believe Karen is a two face jerks but, sadly, they existed (as shown in some comments here).
It's sad that people nowadays has low literacy level that they can't read between the lines and need everything explained to them in details.