Why is everyone treating her like she's an idiot?
She worked out her parents were trash instantly and were planning on taking the money from her and leaving her with nothing.
And she's literally said she isn't going to give them anything.
But there's a fortune on the table, and she's a mercenary. Of course she'd be willing to at least see if she can get some, and if she needs to go through some arrogant, beloved, pampered noble girl who's never worked a day in her life to get it, she would probably give it a shot.
The fact that our first FL is not like that at all would probably change her mind.