From what I remember, the astronaut made first contact with a race of felines that live on the other side of the Galaxy. They had always been able to see Earth, but Earth couldn't see them because they were blocked by the Sun. There are various corporations that do drilling on various asteroids and the feline race helps in saving someone, or stopping an explosion at one of these complexes.
After this (possibly in a second book) she comes back to Earth and is the ambassador to the feline race because they know her. This is upsetting for her because she had worked so hard to become an astronaut, but had a very short career because of this incident. She ends up getting some sort of connection with them, and takes on some of their characteristics.
I think this connection followed some sort of either transformation or psychic episode they were able to induce in her on their ship, where she was able to see what it was like to be one of them. The alien technology is way more advanced than the human, and they are stronger and faster as well.
A final note, I recall the female astronaut having red hair.