Novel Ident: SF story with female chromed android from future temporally follows nemesis robot back into present

A book I once owned and read back in late-80's or early-90's that I have not been able to identify title & author for: It was a SF story concerning two opposing androids/cyborgs/robots from earth's future of constant warfare, possibly when mankind is all but gone. One of the androids is feminine with chromed-appearance, the other masculine (can't recall appearance) and possibly named "Omicron". The feminine android temporally travels from future to present-day US in pursuit of Omicron. The fem-android was purposefully designed to combat the type of android/robot that is Omicron. She has no weaponry, while Omicron has several such forms, yet she is reflectively-immune to all his destructive devices.

Omicron, low on energy reserves, seeks out a location of underground nuke test in order to be present at the site and absorb various energies released in the detonation.

A clever but down-on-his-luck good guy "falls in love" with the fem-android, and enlists his friends/adoptive parents (an old couple, museum caretakers, the old man owning a huge 'elephant' rifle) to help her defeat Omicron.

Near the end upon confronting Omicron, she employs her only means of stopping Omicron, by grappling him in an immobilizing hold... planning to maintain the hold indefinitely by shutting down.