And? The father is making shady deals. Whose to say these deals aren't funding an organization to take out the Prince. Use her then to try and get closer to the Royal family. Her Family doesn't need to have the money, just someone they are working with. They could have convinced her to work with them by presenting it as a way to increase her standing. All he said was that she might have a connection, not that she was responsible. She could be working in league with other houses. Or one of the numerous people her dad has been making shady deals with. which he clearly has the money to make shady deals with.
I'll also reiterate my earlier point, would you really put a person you thought was in league with an assassin in the same room as the target? She had just dodged a question about how she noticed the assassin before she even saw him, it's suspicious. Bringing up that she's possibly connected would be a way to get her to panic and reveal the truth, like overhearing about the attempt and using it for her own gain, or that she can read auras and noticed it.