Well, crap, she won't be able to follow her as easily - though given Sunnydale traffic she's gonna try her best.

She memorizes as much as she can about the make, model, and plates.

It is brown, and of a tiresomely practical style.  The shapeshifter begins driving away; she'll be able to keep up for a little while, but once they get into residential areas the traffic lightens enough for the car to get away.

Well, she knows an approximate residential area... Which honestly doesn't narrow down the search much. Crap.

She starts heading for school. Giles should be staying after...

He is in fact in the Sunnydale High library when she checks.

"So! G-man, potential problem!" she calls out once she's sure no one else is there.

"Oh dear, another one?"

"Pretty much! Some weird shapeshifter attacked me. I stabbed him until he ran off, then he got on the phone with I'm guessing Vanessa. Knew I was the Slayer."

"At least it wasn't some third player... what manner of shapeshifter, exactly?  Is there anything you could use to identify or track him?"

She lists everything she knows.

As she goes over the shapeshifter's discernible anatomy, he retrieves a few demonological references and asks clarifying questions about things like flesh consistency and interstitial fluids.

"Ah, here we are," he says.  "Commonly called ragdoll demons, their name for themselves has phonemes we'd be hard-pressed to produce - "

He notes down the make and model and license plate number.  "I can give this information to my police contact and see if she can track him down."

"Do you have any hypothesis as to how he found you?"

"Not. Really? He didn't talk to me, just rushed me."

He taps his cheek pensively.  "You haven't been doing anything obviously superhuman with any regularity, have you?"

"No? ...Okay I'm keeping the parkour in human ranges but people might not realize that."

"I suppose if a new teenage girl appears on the Hellmouth and publicly exhibits even human-realistic impressive athletic ability, it's an obvious sort of guess.  I think we have to assume that Vanessa has positively identified Nausicaa Uzun as the Slayer."

"...Yeah. Crap. We'll have to - try to stop her faster I guess?"

"And make you less findable in the meantime.  If they can't locate your motel room, it might be a good time to arrange that extended absence from school."

"Would give me more time to look, too."

"Yes.  Can your parents be persuaded to corroborate the story that you've got a bad bout of flu?"

"Maybe? I mean, they get the vampires are a threat..."

"Can you guess, if they don't, the extent and nature of the action they are likely to take against you if you simply stop attending school?  The faculty may not bother contacting the police, for example, but will they?"

She shakes her head. "No. They won't. They'll probably just be concerned and worried and a bit frustrated."

He nods.  "It's a fallback plan, then.  I will be happy to offer you safe harbor during the day if necessary."

"I don't think it'll get that bad. Still - guess I should head to the motel and talk to them? Uh, should I head back here or call you or what once I have?"

"It may be best for you to stay away from campus for the time being.  It is one of the first places they will guess that a Slayer with a public identity will be.  You can call me, if you like, or we can reconvene elsewhere."

"Call with fall-back meeting place?"