Why does Victor refuse to make a female monster?

Concerning Victor's refusal to make a female in Shelley's Frankenstein, actually, Victor eventually agrees to make a female.  At first he refuses, but then he agrees.  He travels to England to learn from experts there, then travels to Scotland and finds an isolated area to work.  He has the female partially built, when

I trembled, and my heart failed within me; when, on looking up, I saw, by the light of the moon, the daemon at the casement.

The "monster" surprises Victor at the door of the cottage.  Victor has a knee-jerk reaction to the look on the monster's face:

As I looked on him, his countenance expressed the utmost extent of malice and treachery.  I thought with a sensation of madness on my promise of creating another like to him, and trembling with passion, tore to pieces the thing on which I was engaged.

So his "refusal" to make a female is actually a passion-filled gut reaction to the monster's facial expression.  It's not reasoned out, but, instead, is an emotional reaction to the monster's surprise presence at his door.