Will it help my transfer chances to take summer classes at Stanford

So, summer classes won’t help for admission. But I think they will help to know how my daughter will fit in the environment.

I am interested in knowing how intense they are? Are they regular Stanford classes or for high shool students? My daughter is invited to attend. She is currently top of her Junior class of ~500. I am not sure if this would affect her GPA and rank in high school in case they are hard even for Stanford students. Does it worth the time and money? (OOS)