Beyond Those Distant Stars — John B. Rosenman

Alien invaders have all but destroyed humanity. Stella McMasters, a retired naval officer, yearns to get in the war but knows she'll never get a chance. Then amazing things start to happen. After saving a comrade's life during a meltdown that almost kills her, physicians remove her radioactive flesh and turn her into a superhuman cyborg. She is then given command of her first ship and, against her better judgment, falls in love with its charismatic pilot. On their way to join the Empire's last line of defense, Stella runs right into an enemy vessel. For the first time ever, the mysterious invaders invite humans aboard. Should Stella accept, or run? Can she avoid a crushing defeat and save humanity in the process?