There are lots of ways to identify a person, but she needs to find one she can use with only the information she has about Bella. Just on the off chance that there are fewer Swans out there than Peregrines, she tries "Bella Swan" and "Isabella Swan", not really expecting either to work.

They don't!

Can she perhaps find a picture of Bella somewhere? High school newsletter on Google Images, Avalon journalist with fast reflexes?

It does not seem that she can!

Just as well that she checked before drawing another diagram to use trying a photo of her dad, then. How about "The nearest person with the first name Jonathan and the last name Peregrine"?

That works!

Alright! Now for the creepy stalker version: nearest person with the first name Isabella and the last name Swan?

Here's a latitude and longitude sans cardinal directions.

She isn't about to drop in on any of the four potential locations without some way to scry first and make sure it's a good time to say hello, but she's curious. Where's the northern and western hemisphere instance of those coordinates, roughly?

Phoenix, Arizona; middle of the ocean; middle of the ocean; Nanzhao, Nanyang, Henan, China.

Unless linguistic talent is among the many things she was hiding, Bella's probably in Arizona. Neat. Now to get scrying working, so she can look ahead instead of just teleporting blindly. She uses the big [light, control, knowledge] diagram from her early drafts of the species detector and tries for an exhaustive description.

"Cause to appear on this paper an image of [Margaret's current latitude and longitude] as viewed from six feet above ground level, looking down, covering the area of a human visual field and scaled such that the entire image fits on this paper." If it needs a more sophisticated description of how to tune the "camera" she's going to want a book on optics.

It does not work.

"Cause to appear on this paper an image of [Margaret's current latitude and longitude] as viewed from the lowest point with at least three feet of uninterrupted air below it, looking down, covering the area of a human visual field and scaled such that the entire image fits on this paper." 

Nope!

Maybe she can test everything except the camera settings and see if she can get an image at all. She sticks a paperweight and her right hand on the diagram and her left hand in the air.

"Cause to appear on this paper an image of the paperweight touching the diagram, as viewed from one inch below the left index fingertip of the person touching the diagram, to scale."

Nope!

"Cause to appear on this paper an image of the paperweight touching the diagram, as viewed from one inch below the left index fingertip of the person touching the diagram, such that the whole image is four inches across."

No can do!

Maybe she needs to buy that optics textbook after all. Or maybe it's a problem with translating from a full-color image to singed paper. She cuts a square a few inches on a side out of a tourist map she had lying around, puts it on the diagram, and tries, "Replicate the image on the map on the other piece of paper, in the same orientation and at one-to-one scale."

It can do that. In full color, even.

Oh, nice! Does it appear to have conjured ink or changed the color of the paper itself or what?

Hard to tell precisely, but the image doesn't bleed through.

Not important anyway. She goes to the library and reads about optics, and the human visual system, and cameras, and eventually develops a theory.

The magic can borrow her handwriting and understand where her hands are, but vision is a lot more complicated. The images formed on her retina and in her brain aren't the same sort of image you get on paper. So maybe it can't copy her vision, but would be able to copy a camera.

This theory expresses itself in a bunch of French notes (actually, all her notes are in French lately; it's good practice and deters shoulder-surfers). On the way home she buys a camera--a Polaroid instant one, just to be safe. She puts it on a new diagram, sticks out a hand, and tries, "replicate at one to one scale on the paper the fully-developed form of the image this camera would take from the location of my left hand, pointing down".

That works.

Finally! It's a wonder anyone who isn't a dragon ever does this stuff. Which raises questions about the other runecasting enthusiast she knows, who clearly isn't a dragon but also clearly has stuff going on she isn't talking about publicly.

Speaking of Bella, time to try scrying her. "Replicate at one to one scale on the paper the fully-developed form of the image this camera would take from three feet above the head of the nearest person with the first name Isabella and the last name Swan, pointing down".