GAP year -- grades and tests?

My daughter (senior now) is planning to take a gap year and will be applying for college next fall. Her SAT scores were not as high as she would have liked (1420, balanced). She can re-take it this Fall or Spring, but she is busy with AP classes etc. – is it true that she can not take it in summer after HS graduation? Are senior grades calculated in her GPA when she applies after HS? Any advice as we embark on this new idea and begin to collect information. Thanks!