Barbara Paul’s 1979 Pillars of Salt is a time travel novel.
Transporting physical matter into the past is, of course, impossible. However, projecting consciousness into the bodies of past humans merely requires the correct technology. Mid-21st-century America (and presumably the rest of the planet) possesses the means and uses it freely.
Angie Patterson believes she is quite familiar with the mechanics of time travel. A foray into Elizabethan England reveals to her something of which she (and most other travelers) had been utterly unaware.