It's a recent science fiction book, protagonist is a teenage girl involved in a space program with rigorous testing.
Book was read a year or two ago, so it is a recent title.
Here's what I remember: teenage girl protagonist is chosen to intern or work at a space program. She and the other teenagers are put thru a series of physical and psychological tests, including underwater exercises and time in a space suit that is filled with a breathable gel. Various kids fail at different points, but the girl succeeds. At the end the girl falls for a boy who ends up being from a different planet.