The Jurassic Park III Film Script reveals more of Cheryl:
we see CHERYL, 21, a junior at junior of State. She's one of a dozen COLLEGE STUDENTS working at the site, and the one most smitten with her supervisor (Billy Brennan).
She asked Billy to better tell the difference between a rock and a fossil. He runs her bare fingers over the two different patches, showing her that rock is rough and fossil is smooth.
In the script the two start to flirt. Cheryl runs her finger along his stubbly chin, "rough", and along his lips, "smooth". Billy may not have started this flirtation, but he's not ending it either.
The two stop talking when Dr. Grant arrives at the site.