Her brains WILL grow back. She would not be offered summer options if WP didn't want her. Many, many USNA plebes find themselves at summer school taking Calc, Chem, or both. The SAs understand this is a huge transition in depth and intensity of academics mixed in with a hundred other new sources of pressure.
Support her with love and understanding, and trust her to make her way through. It can be hugely unsettling for those who were undoubtedly HS stars, to find out someone gets the C, D or F on exams and grades, and it turns out to be them. She will figure it out, will succeed and find her footing, and her pride and confidence will be fierce.
The "my brains grew back" phrase is a memorable one from a basketball player (I was the officer rep for USNA women's team) who struggled mightily her first two years and spent leave blocks at summer school. Then, a switch flipped, she found her stride, got Dant's List, and sailed smoothly to graduation.