She should be really proud. A lot of women have impostor syndrome, it's a habit that needs to change.
Do the (primarily white male) CEOs of failing companies show one iota of remorse for their fat-cat pensions, bonuses and golden handshakes? No.
Do the privileged private school kids worry that they are only getting their spots in uni, their future careers, and their places in many sports professions because of their advantages? No.
So, sure, she benefits from grade inflation. Big deal. Life very occasionally does you a favour - she should take it, be thankful, and spend her life making the most of it.
Perhaps she'll turn her educational advantage to good use, and become a scientist or a doctor or a human rights lawyer.
Encourage her to own her success with pride, and to move forward in her life with confidence.