Her Last Hope by Blake Pierce

FBI Agent Rachel Gift, 33, unparalleled for her ability to enter the minds of serial killers, is a rising star in the Behavioral Crimes Unit—until a routine doctor visit reveals she has but a few months left to live.

Not wishing to burden others with her pain, Rachel decides, agonizing as it is, not to tell anyone—not even her boss, her partner, her husband, or her seven-year-old daughter. She wants to go down fighting, and to take as many serial killers with her as she can.
A serial killer is targeting vulnerable organ donors with seemingly no rhyme or reason, and Rachel is locked in a furious race against time to find the connection between the murders and stop him before he strikes again.

But Rachel herself is faltering, beginning to succumb to her illness.
Can she keep it together long enough to catch this killer before her own death? And can she keep her own demons—and her own traumatic past—at bay?