Quote - I create a null in the same location as the camera, once the camera is where I want it and locked down to prevent accidental movement between renders.

Having the eyes point at that seems to work better, and allows some adjustment without messing with the camera.

The null object uses less memory than a sphere or random prop, too

Well, if by that you mean Create>New Null>Apply Active Viewport Settings-Camera 1>Accept

but before that I have to position her eyes manually towards me or the camera as precisely as possible as I spend many hours trying to do.

And how do you lock the camera down so it can't be moved?