What's one word for the phrase 'the act of taking your head back on seeing something strange'?

This is not a single word, but it works for your purposes: taken aback

This can be used in the figurative sense (and usually is), meaning:

(MW.com)

to make a strong impression on (someone) with something unexpected

It's origin is a nautical term:

(Etymonline)

Now surviving mainly in taken aback, which originally was a nautical expression in reference to a vessel's square sails when a sudden change of wind flattens them back against the masts and stops the forward motion (1754).

Literally, it means being pushed backward (as the head in your example) or halted in your tracks.

Start, perhaps - To (cause to) make a sudden movement, and related senses.(OED)

To make a sudden movement, esp. of part of one's body, as to avoid a blow or perceived threat; to flinch or recoil from something in alarm or repugnance. Chiefly with from or with adverbs (as aback, aside, away, back, etc.). Also with the part of the body as subject. (OED)

To undergo a sudden involuntary movement of the body, resulting from surprise, fright, sudden pain, etc.; (sometimes without implication of actual movement) to feel startled or momentarily perturbed, as at a sudden realization. (OED)

So,... "She turned away and started at the sight of the filled porcelain."