This Would Be Paradise: Book 3 by N D Iverson

After a shocking betrayal, Bailey finds herself taken by mercenaries and handed over to an even worse group of monsters. Led by a cold and calculating scientist, they see immune people as the answer to the infection—no more than test subjects to use for their own gains. Bailey soon realizes that escape may be harder than she expected, even when a familiar face is thrown back into her life. Together, they must attempt to rally the troops and escape their forced imprisonment—or face heinous experiments, all done in the name of finding a vaccine.

In the series finale, Bailey is pushed to the limit as she sees just how far she will go to protect herself and her friends. Will she stand her ground, or will the new world take her down with it?