Wrong Side of Time by J.J. Green

When the greatest minds in the galaxy can't solve a problem through logic or reason, they call Carrie Hatchett.

Carrie and her reluctant sidekick, Dave, have succeeded in driving the evil mechanical aliens, the placktoids, to their only remaining hiding place—the past. But the danger isn't over. The Transgalactic Council suspect the placktoids are trying to change the course of history and re-emerge as rulers of the galaxy.

Carrie and Dave are assigned to defeat them, but even attacks from her psychotic cat can't prepare them for the challenges they face when they travel back in time to the placktoid planet: searing temperatures, a barren landscape and primitive robots with OCD. And waiting in the wings is the placktoid High Commander, whose 3D printing ability is lethal.

Innocently optimistic Carrie needs to recognise what's staring her in the face if she's to defeat the placktoids and avoid being trapped in the past forever.